Source: Georgi Plekhanov, Selected Philosophical Works, Volume 3 (Progress Publishers, Moscow, 1976), pp 424-54. Prepared for the Marxist Internet Archive by Paul Flewers.
Moscow Editor’s Note: ‘The article on Joseph Petzoldt’s book Das Weltproblem von Positivistischem Standpunkte Aus (The Problem of the World from the Standpoint of Positivism) was written by Plekhanov for the collection of articles From Defence to Attack, which appeared in 1910. Joseph Petzoldt (1862-1929) — German idealist philosopher, pupil of Mach and Avenarius.’
Review of: Joseph Petzoldt, The Problem of the World from the Standpoint of Positivism (translated from the German by RL, edited by P Yushkevich, Shipovnik Publishers, St Petersburg, 1909).
This book is apparently destined to have conspicuous success among certain circles of our reading public. First, it provides an exposition of a philosophy now fashionable in these circles. According to J Petzoldt, the aim of the book is
... to explain the usually falsely construed central point of the positivist understanding of the world, substantiated by Wilhelm Schuppe, Ernst Mach and Richard Avenarius,  and to comprehend this world-outlook as historically necessary, logically inevitable and therefore, most probably, final in its essential features. (p vi)
That will suffice at present to attract the attention of numerous readers to the work concerned; and apart from this, Petzoldt knows how to write with great clarity. True, it is not that scrupulous clarity which helps one to overcome the difficulties of the subject, but that deceptive clarity which tends to conceal them from the reader. It is the clarity of very superficial thinking, which brings its work to a halt just where its main task begins. But this is not a bad thing. A very superficial philosophy is just what we need at present. The reading public which is buying up the works of the Bogdanovs, Valentinovs and Yushkeviches,  and leaving unsold in book stores such a splendid work as Engels’ Ludwig Feuerbach — this reading public does not have and never will have the slightest need of profound philosophical works. Hence there is every reason to expect that Petzoldt’s The Problem of the World will quickly run into several editions.
But since I do not share the philosophical infatuation fashionable just now, and since I am not content with the sort of clarity that conceals the difficulties of a subject instead of helping to overcome them, I consider it worthwhile subjecting to criticism the principal ideas set forth in Petzoldt’s book. Who can tell? Perhaps I shall find a reader who prefers to use his own brains for thinking rather than to follow the latest fashion in philosophy. Anything can happen in this world!
The fundamental idea of Petzoldt’s whole book is expressed by the author himself in the following words:
There is no world-in-itself, there is only a world for us. Its elements are not atoms and not other absolute beings, but the ‘sensations’ of colour, sound, touch, space, time, etc. In spite of this, things are not only subjective, not only phenomena of consciousness — on the contrary, we must conceive of the parts of our environment, composed of these elements, as existing in the same manner both at the moment of perception and when we no longer perceive them. (p v)
I leave aside for the time being the question of what is meant exactly by the proposition that ‘sensations’ must be regarded as fundamental elements of the world. I will dwell at present on the following: ‘There is no world-in-itself, there is only a world for us.’ So Petzoldt assures us. We believe him and say: ‘Since there is no world-in-itself, there is nothing objective; all things are subjective and the world is only our idea of it.’ We wish to be consistent, but Petzoldt does not want that. No, he objects, in spite of there being only the world for us, this world is not only our idea of it, and things are not only subjective; they are not only phenomena of our consciousness. Let us admit that too: we believe Petzoldt. But what is the meaning of: things are not only subjective, they are not only phenomena of our consciousness? It means that in spite of there being only the ‘world for us’, there is also the ‘world-in-itself’. But if there is the world-in-itself, then Petzoldt is wrong in proclaiming that the world-in-itself does not exist. What are we to do now? What are we to believe? To extricate us from this difficulty, our author advises us, as we know, to conceive of the parts of our environment as ‘existing in the same manner both at the moment of perception and when we no longer perceive them’. But unfortunately this advice does not in the least get us out of our difficulties. The question here is not what things are like at the moment we do not perceive them, but whether they exist independently of our perception. According to Petzoldt, this question can only be answered affirmatively; yes, things exist independently of our perception, that is to say, they do not cease to be when we stop perceiving them. But this reply does not correspond to what Petzoldt himself thinks and says. To say that a thing does not cease to exist even when we cease to perceive it is the same as saying that it has being which does not cease even when the thing no longer exists ‘for us’. Then what sort of being is this? The answer is as clear as twice two are four: it is being-in-itself. But Petzoldt assures us that there is no being-in-itself. Again I ask: what are we to do, which Petzoldt are we to believe? The Petzoldt who reiterates that there is ‘no world-in-itself’ or the one who proves that the world exists even independently of our perception of it, that is, that there is a world-in-itself? This is a question truly in the mood of Hamlet! Let us work out the answer for ourselves, since it is useless to expect help from our author — he himself does not ‘sense’ the contradiction in which he is so ludicrously struggling.
There is no world-in-itself, there is only the world for us; there is not only the world for us, there is also the world-in-itself. Such is the antinomy in which Petzoldt is entangled. In order to see where exactly he committed his sin against logic, we shall have to examine separately what he says in favour of each of the two sides of the antinomy.
There is no world-in-itself, there is only the world for us. Why does Petzoldt think so?
Because he believes the doctrine of substance to be completely untenable. He says:
The idea of substance contradicts experience. Not in a single thing do we find such a something that underlies the thing, something that would constitute its inner essence and remain unaltered in it under all changes determined by time and circumstances... We can only resolve things into a number of exclusively changeable qualities — which psychology calls sensations, into what can be seen, what can be touched, what produces sound, what has taste, and so on, which in the course of time are replaced in everything by something else which can be seen, touched, and so on; but never, even with the most perfect instruments, do we discover a part which is indefinable by its quality, to say nothing of such an indefinable something underlying all things. It is a pure thought-thing about which reality knows nothing. (pp 60-61)
Further, in characterising the development of the philosophy of antiquity, Petzoldt asserts that the notion of substance leads inevitably to dualism:
Heraclitus and Parmenides,  however differently they conceived of what properly speaking, that is which only is present in appearance — being in a state of rest, or becoming which knows no rest — nevertheless agreed that it is the eye and the ear and the senses in general which conjure up before us a false picture of the world and are the cause of all error...; that we can expect truth from reason only. This dualism also is an inevitable consequence of the idea of substance. (p 93)
Somewhat further on it appears that the idea of substance, developing in the most logical way, changes into the idea of something which is within things much in the same way as the soul is within the body according to the views of the animists:
Since substance, in the final analysis, is everything, then it must also contain the principle of motion and of change in general; and as it, generally speaking, cannot be perceived by the senses — on the contrary, visual appearance, appearance perceived by the senses conceals it from us, but since it nevertheless is the essential in every thing, then it is hidden in the thing, as the soul, as it were, of the thing. (pp 113-14)
This, of course, is quite untrue. But the important point to me is not that it is untrue but that it seems to Petzoldt to be true. I set myself the task of expounding in his own words the principal arguments he advances in favour of the thesis: there is no world-in-itself, there is only a world for us. To accomplish this task, I shall have to make one more extract in which the question of substance is also dealt with:
The knowledge of the real world could have developed in a straight line after Protagoras  only if we had been able to free ourselves completely from the idea of substance, if we had realised that the strong tendency of philosophical teachings to diverge was based only on fruitless efforts to find an imaginary absolute world, only on the unjustified belief in an absolute being, an absolute truth, not dependent upon anything subjective, on the delusion that behind the many there must lie a one, behind the heterogeneity of being and reality — something homogeneous, immutable, persistent. Had Protagoras omitted or been unable to cast this conception, which he had arrived at more by brilliant intuition than by logical analysis, into propositions unassailable in all respects and thereby made it relatively easy to pass them on, it would have been the task of his wise followers to elevate the new knowledge to the full light of consciousness and think it out to the end. (p 110)
Now we are sufficiently well acquainted with the arguments advanced by Petzoldt in defence of his thesis. It must be admitted that within the limits of this defence our author is logical after his own fashion. Actually, to say that there is no such thing as substance is to assert that there is no world-in-itself, but only a world for us, for the perceiving subjects. But who exactly are these ‘we’, these perceiving subjects? Should we not attach substantial significance to them? Must we not assume that the human ego is the substance underlying phenomena? If Petzoldt would say ‘yes’ to these questions, that tiny word would mean the total renunciation of all he has said against the existence of substance. But, like his teachers — Mach, Avenarius and Schuppe — he will not pronounce that tiny word. He will not accord substantial significance to the human ego. He says:
Protagoras knew already that the soul is nothing outside of its content and, consequently, this content does not require a special vehicle. He was also aware that the sensual perceptions are the basis of the spiritual elements, with which everything else is associated. Thus he held in principle the point of view of our contemporary ‘psychology without the soul’, and thus the prerequisites were provided for fruitful investigation of the facts of the soul. (p 111)
Here again he is logical; but if there is no ‘ego’ as a substance undergoing sensations, and no thing-in-itself as a substance causing these sensations, what are we left with? We are left with nothing but these sensations, which are thus transformed into the basic elements of the world. He who denies the conceptional substance comes logically to ‘Machism’.
Having substantiated his thesis, Petzoldt breaks into a song of victory. He says:
Once science has fully overcome the idea of substance, a whole period of thought, stretching over many thousands of years, has been brought to an end. Philosophy’s main previous task has been resolved. The history of philosophy in its former sense has ended, since it was primarily the history of the idea of substance, the history of metaphysics. (pp 211-12)
In a certain sense, this is true. If the concept of substance has been eliminated, then by the very fact the most important of the problems with which philosophy had struggled so long has also been eliminated. Among these first place is held by the problems of the subject, the object and their mutual relationship. If Petzoldt’s ‘positivism’ entitles us to dispense with these most difficult problems as empty ‘metaphysical’ concoctions, it lifts a considerable load off the shoulders of the philosopher. Unfortunately, it does not and cannot entitle us to disregard these problems. We very clearly see this from the example of Petzoldt himself, whose thesis is followed by an antithesis.
There is not only a world for us; there is also a world-in-itself. Our author proves this at least as successfully as he has substantiated his thesis.
He rejects decisively Kant’s concept of reason dictating its laws to nature:
‘It is not thinking that is determined by things, but things by thinking’, he exclaims. That is the proud and fateful Copernican reversal through which the rationalistic passion, held in check in Kant by his wide knowledge of and interest in the natural sciences, was to be unfettered anew in his successors of theological origin. (p 181)
That is quite true. And Petzoldt’s following remark is no less true:
If the laws governing phenomena originated only in the brain, then we are at a loss to answer the question: how was the development of organisms possible before the formation of the brain? From this it is clear that whoever holds that things are determined by thinking delivers himself body and soul to the devil of transcendentalism, of that metaphysics which Kant most earnestly wished to see banished from all genuine science, although he himself had completely fallen to it. (p 182)
But if it is absurd to say that things are determined by thinking, it is no less absurd to assert that they are determined by sensation; and if he who says that they are determined by thinking delivers himself ‘body and soul to the devil of transcendentalism’, then he who contends that things are determined by sensation cannot hope to escape the same terrible fate. To the first of these two rather poor thinkers, it is indeed necessary to put the question: ‘How was the development of organisms possible before the formation of the brain?’ But it is also necessary to ask a similar question of the second of our poor thinkers: how was the development of the universe possible before the formation of organisms capable of having sensations? He can have only one answer to this question: the universe then consisted of those elements which later, in the organism, were to become sensations. But this is nothing more than the height of ‘transcendentalism'!
However, that by the way. My task here is not to refute Petzoldt but to indicate the arguments he uses to prove the correctness of his antithesis. Let us follow him.
The most important of these arguments is contained, in my opinion, in the following remarkable passage:
Let us try then to draw as clear a picture as possible of what results when we cease to believe in the existence of things independent of ourselves. I have only to close my eyes, and all the objects I now see before me will vanish not only from the sphere of my perception but vanish altogether. I have only to open my eyes again and they are there anew; they arise again. In deep sleep the universe is annihilated, and when I awake it arises again out of absolute nothingness. Is it not clear that ideas of such possibilities can enter the head only of one accustomed to think of everything in terms of ideas which come and go? Could anyone lend himself to such fancies who, from the very beginning, ascribes just as much independent existence to the physical, corporeal, ‘non-ego’ as he does to the psychical, the soul, the ‘ego'? Where in this case is the consideration for the fact that independently of whether my eyes are open, things always appear again either where they were or in another place independent of my thinking, for the fact that there is a fully consistent and law-regulated connection between the things perceived? (pp 197-98)
This is a triumphant refutation of the views of people who refuse ‘to believe in the independent existence of things’, that is to say, in the existence of the world-in-itself. But Petzoldt does not rest on his laurels. He gives no quarter to the idealism he has vanquished, and finishes it off with arguments that combine overwhelming logical thoroughness with the acidity of malicious satire:
Of course [he continues], the true idealist cannot be content with his experience alone. In fact, the present moment is all that he is sure of. It is in no way established for him that the world and human history exist, that something must develop, that he himself was once a child and grew up physically and mentally, that he lived yesterday — more than that, that he was living a moment ago — all this might perhaps be but a delusion, only a chain of ideas being lived through at the given moment, a clever hypothesis created for the sole purpose of interpreting logically that which is being perceived at the present moment — just try to prove to him the opposite! (p 198)
Whoever does not wish to get lost in this labyrinth of absurdities must certainly recognise that things exist independently of our notions of them, that is to say, not only for us, that is, also in themselves. Which is what was to be proved. But if the antithesis is proved, what about the thesis? If the world exists also in itself, if it existed already prior to the coming of man, that is, if it exists not only for us, how can Petzoldt claim that it exists only for us? We now know how the thesis is proved and how the antithesis is proved: we are familiar with both sides of the antinomy, but we do not see any way out of it. There is not even a hint of synthesis, and this absence of a way out is a bitter reproach to our logic. A way out must be found, cost what it may!
All the difficulties of conceiving of the range of elements of the optical and tactile qualities (such as red, blue, round, angular, prismatic, conical, hard, soft, rough, etc) as existing outside of our perceptions of them [says Petzoldt] spring from the difficulty we have in detaching ourselves from the concept of absolute being and immersing ourselves sufficiently in the idea of relative existence. Until recent times, the great idea of Protagoras exerted only very insignificant influence. Even Hume failed because he could not find a way to relativism in principle. In his works (as in those of Hobbes before him) we find only feeble rudiments of relativism, and only Mach and Avenarius rediscovered the deeply buried truth and made it the main factor in their world outlook. (pp 199-200) 
This passage gives us to understand that the way out of the antinomy wherein we have lost ourselves must be sought, not in the direction of the antithesis, but in that of the thesis. The world also exists independently of us, but this existence can in no way be acknowledged as being-in-itself. The world exists not only for us, but its existence not only for us is identical with its existence only for us. We assert the antithesis but we do so only for the greater glory of the thesis. Such is the solution implicit in the passage just quoted from Petzoldt. Do you think it is an impossible solution? You are mistaken. You are not well enough acquainted with ‘modern’ positivism.  Listen to Petzoldt:
Imagine observer A standing before a blossoming apple-tree and describing to us what he sees. His description coincides with our own observations. Let us assume that he turns away from the tree, and that he no longer perceives it. This does not affect in the least our own perception of the tree. The tree goes on existing for us, and in its existence for us it is independent of A’s perception. Moreover, by eliminating the concept of substance we cease to make a distinction between our perception, the ‘image’ of the tree in our perception, and the perceived part of the tree itself: in perception we apprehend the object immediately in its perceptible parts. If we now assume that observer A is in principle entirely like ourselves, that he is a sensitive and thinking person like ourselves, and that in principle we find ourselves exactly in the same position in relation to the tree as he, we at the same time also assume the existence of the tree independently of our own perception of it; just as the tree continued to exist after A had turned away from it, so it will go on existing if we ourselves turn away from it. But if we deny or doubt this independent existence, we also deny or doubt the existence of other people. So long as we do not decide to do this, we have no possibility of denying the continued existence of things even if we no longer perceive them. (p 200)
Now you see how the contest between thesis and antithesis is brought to an end. You understand also why it ends in favour of the thesis. Having eliminated the concept of substance, we cease to make any distinction between our ‘image’ in the perception of the tree and the part of the tree perceived. The dualism of being-in-itself and being-for-us has given way to the kind of monism in which being-in-itself is indistinguishable from being-for-us. True, this monism smacks strongly of extreme subjective idealism: if we do not differentiate being-in-itself from being-in-our-perception, the existence of the ‘blossoming apple-tree’ must be considered to cease as soon as we turn our backs on it, that is, when we cease to perceive it. However, this would hold true only in the case when we denied the existence of other people or, at least, had doubted it. But we do not commit this sin at all. Quite the contrary! Without a moment’s hesitation, we ‘imagine’ observer A who perceives the ‘blossoming apple-tree’ on our behalf while we stand with our backs to it. Since the tree continues to exist in his perception of it, it follows that it exists independently of us; which means that we have maintained all the lawful rights of the antithesis. But, on the other hand, since the tree’s existence independently of ‘us’ is no more than its existence in the perception of observer A, that is to say, existence only for ‘us’, it follows that the tree has no being-in-itself. In other words, it turns out that, although the antithesis seems to have maintained all its lawful rights, so brilliantly defended by Petzoldt, the contest was won, not by the antithesis, but by the thesis. How easily this truly perplexing affair has been resolved! All that was required was the use in one and the same argument of the word ‘we’ in two different senses: at first (in proving the antithesis) in the sense of a pronoun in the first person singular, that is, instead of ‘I’, and then (from the moment observer A came on the scene) in the sense of the same pronoun in the first person plural, that is, in the sense of the proper ‘we’ signifying not one person but many. Eins, zwei, drei, Geschwindigkeit ist keine Hexerei! 
But no matter how amazing our author’s Geschwindigkeit, I take the liberty of reminding him of the terrifying question he asked when defending his antithesis and which he used like the cudgel of some hero of old to strike down the idealists: ‘How was the development of organisms possible before the formation of the brain?’ In the present instance this question takes on the following form: ‘How was the development of “blossoming” trees possible before the appearance of observer A, who went on looking at one of them at least, while “we” and Mr Petzoldt turned our backs on it?’ There can only be two possible answers to this terrifying question. One of them runs: before ‘we’ and observer A appeared there were no trees. This reply has the great disadvantage of being in contradiction to the conclusions of geology, or to be more exact, of paleophytology; but on the other hand it also has the great advantage of being fully in accord with the fundamental principle of Petzoldt’s book, viz: there is no being-in-itself, the world exists only for us. The other possible reply has a meaning directly opposite to the first: the tree existed already at the time when ‘we’ did not yet exist. This reply is fully confirmed by the conclusions of paleophytology but causes ‘us’ and Mr Petzoldt this unpleasantness, that it knocks down like a house of cards the whole doctrine of ‘modern’ positivism. For if trees really did exist at the time when we did not, that means that the world exists not only for us but also in itself.
Incidentally, if we recognise the independent existence of the world only because we believe in the existence of other people, we continue to stand with both feet on the ground of ‘pure phenomenalism’. But on the admission of Petzoldt himself, ‘pure phenomenalism’ is nothing else than one of the varieties of idealism (see above our author’s contemptuous reference to Auguste Comte and Mill). Therefore, Petzoldt himself must be placed among the idealists.  But his idealism does not acknowledge its own existence and is afraid of its own essence. This is unconscious and cowardly idealism.
This cowardly idealism is imagined to be monism, since it thinks it has eliminated the ‘dualism’ of being-in-itself and being-for-us. But by what manner of logic was this imaginary dualism ‘eliminated'? By admitting that the existence of the object independently of our perception is but its existence in the perception of other people. The blossoming apple-tree exists independently of me: this is proved by its existence not only in my perception but also in that of ‘observer A’ and of other egos. But if it exists in the perception of each of these individuals, without having any ‘being-in-itself’, it must have as many existences as ‘we’ have observers. In place of monism we arrive at something in the nature of a parody of pluralism. But again ‘we’ do not notice this ‘turn of events’, since ‘our’ idealism is not only cowardly but unconscious.
Not without reason is it said: know thyself. Petzoldt’s unconscious idealism has the shortcomings characteristic of idealism in general. But to the shortcomings characteristic of all brands of idealism, Petzoldt adds particular defects caused by its being unconscious. Conscious idealism does not refuse to solve the fundamental question of all modern philosophy, that of the mutual relation of subject and object, although the solution it offers is a bad one. Petzoldt’s unconscious idealism evades the examination of this question on the excuse that the question loses its meaning as soon as we renounce the concept of substance. But just because Petzoldt’s unconscious idealism, which calls itself modern or real positivism, evades the problem of the mutual relation of subject and object, the problem makes itself felt in the most unexpected and unceremonious fashion in the arguments of his followers. Drive it out of the door and it flies in through the window.
Indeed, the reader will recall that, on Petzoldt’s invitation, we imagined observer A to be ‘in principle entirely like ourselves’, and standing beside a blossoming apple-tree. We did so hoping that this gentleman would extricate us from the difficult situation in which we found ourselves, stuck fast in the antinomy between Petzoldt’s thesis and his own antithesis. Now we know that he did us a very doubtful service by taking us directly into the domain of idealism, which Petzoldt and we were repudiating with all our might. But this did not by any means exhaust the unpleasantness caused us by his appearance ‘beside the apple-tree’. His seemingly so innocent appearance there meant, in fact, that we were unexpectedly confronted with the very same question concerning the mutual relations of subject and object which Petzoldt and we were hoping to evade. His appearance demonstrated to us that serious philosophical problems, like things, exist quite independently of whether men wish to consider them or not.
Observer A is ‘in principle entirely like ourselves'; he is just as sensitive and thinking person like ourselves. That is splendid. But one asks: does he exist only ‘for us’ or does he exist also ‘in himself'?
To answer this question, let us assume for a minute that observer A exists only in our imagination (Petzoldt’s invitation to ‘imagine’ observer A did not come by chance). In that case, observer A has, of course, only being ‘for us’ and any being ‘in himself’ is alien to him. He bears no resemblance at all to any kind of substance. That is also good. But what is bad is that in that event his appearance (in our imagination) does not offer us even that illusory solution of the antinomy torturing us which our author had hoped to find in inventing this gentleman; for in this case observer A exists, true, for us, but in no way independently of us. But what is still worse is that if all ‘other people’, like gentleman A, exist only in our imagination, we prove to be incurable solipsists; and then we have not the least right logically to believe in the existence (that is, the real existence, and not as the products of our imagination) of ‘other people’. But even Petzoldt himself, of course, would not dream of agreeing that solipsism can solve a single question of philosophy, or represents anything more than a mockery of philosophy.
It remains for us now to assume that gentleman A exists not only in our imagination. But in making this hypothesis, we recall the sad consequences that followed from the duality of the tiny word ‘we’ when used by Petzoldt. Therefore, we should like, to begin with, to get agreement on terminology.
The word ‘we’ signifies here all people apart from gentleman A. The assumption that gentleman A exists not only in our imagination means that he would exist even if we had no idea of him. Are we entitled to make such an hypothesis? We are not only entitled, we are obliged to make it because, as we have seen, the contrary hypothesis is utterly untenable. But what is the upshot of our now being able to make this hypothesis? The upshot is that gentleman A has not only being ‘for us’ but also being ‘in himself’.
The problem is now solved, but in quite a different way from that planned by Petzoldt. He sought a solution proceeding from the idea that being-in-itself was impossible. It turned out that the question could be solved — short of resorting to the absurdities of solipsism — only on the basis of the idea that it is essential to assume being-in-itself. In other words, if you want to find the truth, you should proceed in the opposite direction to that in which the ‘positivist’ Petzoldt is calling you.
We shall bear that in mind. Now let us go on. What exactly is this being-in-itself which we were compelled to recognise in spite of our author’s arguments? To whom does it apply? It applies, as a matter of fact, to me, to you, to observer A, who, according to Petzoldt, is ‘just as sensitive and thinking person like ourselves’, and, lastly, to all ‘other people’. Now tell me, do you and I and all other people represent something that is beyond the reach of knowledge? It would seem not. Why then did Petzoldt think that being-in-itself is an attribute only of unknowable substance? Simply because he has a wrong notion of being-in-itself. He would like us to believe that he is a positivist in its newest sense, but in fact turns out to be an idealist who clings to an utterly obsolete, utterly bankrupt theory of cognition. This seems improbable, but it only seems so because ‘philosophers’ of the school to which Petzoldt belongs have been shrieking themselves hoarse about their positivism. They were taken at their own valuation, which was very very imprudent.
We have assumed that observer A exists, in spite of the fact that all the rest of mankind have not the foggiest notion of him. Now let us assume that ‘we’ have finally discovered that he does exist. In consequence of this, he has begun to exist ‘for us’. Do ‘we’ have any reason to think that on account of this he has ceased to exist in himself? No, since to discover the existence of gentleman A does not mean to destroy him. If this is so, it turns out that our gentleman now exists in dual form: 1) in himself, 2) for us. In the first instance, he is a thing-in-itself, and in the second instance, he is a phenomenon. Nor can it be otherwise. All that I assert here in regard to observer A, I assert also in regard to you, reader. First of all, you exist in yourself, and, secondly, for me, that is to say, in my imagination. Am I right? Perhaps, if you are a ‘positivist’ in the newest sense, you will find my assertion to be ‘metaphysical’ and will tell me that such duality is ‘unnecessary'?  Maybe you will demand that I repudiate your being-in-itself and acknowledge that you exist only for me, that is to say, in my imagination? I say in advance that I will never agree to this, because if I did, I should arrive at solipsism, and both Petzoldt and I reject solipsism decidedly.
What does all this mean? It simply means that Petzoldt is hopelessly entangled in contradictions and that his ‘positivism’, which promised radically to eliminate the very question of the mutual relation of subject and object, has quite unexpectedly run up against this important question and smashed itself to smithereens.
Now I invite the reader to recall the arguments our author used to defend his thesis.
He said (see above) that the idea of substance contradicts experience, since:
... we can only resolve things into a number of exclusively changeable qualities — which psychology calls sensations... but never, even with the most perfect instruments, do we discover a part which is indefinable by its quality...
This reasoning, which he believes to be irrefutable and to which he returns on almost every page of his book, in fact proves that he himself has not yet emerged from the sphere of an obsolete and truly scholastic theory of cognition.
For people who have outgrown this scholastic theory — for example, the materialists, at whom Petzoldt turns up his nose without the least justification — the question is not whether anything remains after we have ‘resolved’ a thing into its ‘qualities’. According to their doctrine, it is quite ridiculous to pose the question in this way. The quality of a thing is by no means a component part of it. This may be easily verified if we take the example of, say, such a commonly known thing as water. If we resolve this water into its component parts we shall get oxygen and hydrogen. These two elements are component parts of water. But can we describe them as qualities? This would really be excusable only on the part of Gogol’s Poprishchin. 
What do we mean when we refer to the qualities of a thing? Its qualities — or, to use a more common and, in this case, more exact term, its properties — we materialists describe as the capacity of a thing to modify itself in a certain way, under certain conditions, and to induce corresponding modifications in other things connected with it in one way or another. For example, water at 0°C freezes. That capacity to freeze at the temperature mentioned is undoubtedly one of the properties of water. Further: frozen water (ice) coming into contact with one’s body produces certain changes in the condition of the body, frequently leading to illness, for instance, inflammation. This capacity of ice to promote certain processes in one’s body under conditions of more or less continuous contact must also be regarded as its property. Those changes in the state of the body which are produced by contact with ice are accompanied by a sensation of cold. The capacity of ice to arouse this sensation is again called its property. To Petzoldt, all properties of all bodies are ‘reducible’ to sensations. He thinks so because, as we know already, he takes the standpoint of idealism, although he is afraid to admit it either to himself or to others. In fact, sensation is but the subjective side of the process which begins when a given body — shall we say, ice — starts to influence another body organised in a certain way, for example, the human body. For a very long time past, the idealists have been advancing the proposition, in opposition to the materialists, that man is ‘given’ only his sensations and ideas, and that therefore he can know only his sensations and ideas; whereas the things-in-themselves, which, in the opinion of the materialists, are the cause of sensations, are beyond the reach of knowledge. The idealists look upon this proposition as of paramount importance. However, it cannot withstand the faintest breath of serious gnosiological criticism. What does it mean to know a given thing? It means that one must have a correct idea of its properties. This idea of its properties is always based on the sensations we experience when subjected to its influence. Knowledge, like sensation, is always subjective, because the process of cognition is nothing more than the process of forming certain ideas in the subject. One must have a great deal of naïveté in philosophical matters to believe that the discovery of what is presupposed in the very concept of knowledge is a highly important gnosiological revelation. To repeat that our knowledge is subjective is simply tautology. The question is not whether knowledge is subjective: that is self-evident. The question is: can knowledge be true? To put it another way: can the ideas of the properties of a thing formed in the subject correspond to, that is, not contradict, its real properties? This question presents little difficulty when we remember that our ideas of a thing are created on the basis of the sensations we experience when we come into contact with it in some way or other. On the basis of our previous contact with a thing we may have formed an idea of its properties that does not conform to reality; in that case, sooner or later we shall feel this lack of conformity when we again come into contact with the thing. Thus if we thought that water could not solidify — the savage natives of the tropical countries actually have no idea of this property of water — we should realise our mistake at our first opportunity of seeing water freezing. Experience is the judge which decides in the last resort whether the idea of an object formed in the mind of a subject corresponds to the properties of the object. Sometimes the judge needs much time to solve one or other of the innumerable questions of this sort. The old man is sometimes exasperatingly slow. But, generally speaking, the older our judge becomes the more he sheds this defect. Besides, no matter how long he takes to ‘go into it’, he must none the less be recognised as a quite reliable judge. Should the subject’s conceptions, say those of our friend observer A, of the world surrounding him not correspond even to a part of the real properties of the world, he simply could not exist; he would perish in the struggle for existence, in the same way as all other incompatible organisations perish in it. Thus the very fact that subjects exist, that is, exist in reality and not in the heads of some philosophising super-subjects or other — is our guarantee that their knowledge is not only ‘subjective’ but is also true, at least partly, or in other words, that it, at least partly, corresponds to the real properties of the world. This thought could be expressed in another way: the very fact that there exist thinkers who proclaim the unknowability of the external world (that is, the world lying beyond sensations) is our guarantee of its knowability.
Completely at a loss on this question, Petzoldt, being nurtured on idealist prejudices, decided that, if the subject is ‘given’ only his sensations, there is absolutely no need to assume the existence of any kind of external cause for these sensations. He repudiated the existence of things-in-themselves. But after doing so he admitted, as we have seen, the existence of ‘other people’. And by admitting the existence of ‘other people’, he thereby admitted the existence of things-in-themselves, because each given person is, as we have seen, a person (and, consequently, a thing) in himself, and at the same time is a person (and, consequently, a thing) for another, that is, for his fellow-man. There is no dualism of any kind here, no unnecessary duality, since from the time other people came to be, not even one of them, as far as we know, ‘doubled’ himself as a consequence of existing not only in himself (and as a conscious being, for himself) but also for others.  If Petzoldt got himself involved in contradictions, it was precisely because he knew nothing of the materialist theory of cognition. He knew only that idealist gnosiology which claims that knowledge based on sensations is not real knowledge, since it supposedly does not reveal to us the true nature of things, but tells us only about their external appearance. He was simple enough to believe that all thinkers who recognise the existence of things-in-themselves, must be agreed among themselves ‘that it is the eye and the ear and the senses in general which conjure up before us a false picture of the world and are the cause of all error’. In clinging to the utterly mistaken conviction that things which had the property of being-in-themselves could not be perceived by the external senses — ‘on the contrary, appearance perceived by the senses conceals them from us’ — he took up arms against the doctrine of being-in-itself, making the struggle with this doctrine the principal task of philosophy. After what I have said above, reader, about your and my being-in-ourselves, I see no necessity to prove that Petzoldt was mistaken in attributing to all thinkers who acknowledge such being the striving ‘to find an imaginary absolute world’, accompanied by the belief in some kind of absolute being, in some kind of absolute truth that is dependent on nothing subjective. This enormous error, extremely unfortunate in its results, arose from the fact that Petzoldt, as I have already remarked, had a very poor understanding of the materialist theory of cognition, and knew only the idealist gnosiology which, indeed, has committed from time to time — for example, in the person of Plato — all the sins he himself refers to.  And only because he knew so little about the materialist theory of knowledge, which had already acquired a systematised form in the works of Feuerbach, did he turn to Protagoras, whose well-known principle ‘Man is the measure of all things’, won him over by its deceptive simplicity and obviousness. But we already know that this proposition of Protagoras’ was not fated to guide our author out of a maze of insoluble and often highly comic contradictions.
In characterising the philosophy of Parmenides, Petzoldt says reproachfully that it did not even consider the question, ‘whether, and how, the world of appearance, which after all exists in some manner and is governed by laws, is related to the real world of the one which has being’ (p 85). Yet, adds our author, anyone who did not think formally would regard this question as most important. I am very pleased to be able to agree with Petzoldt, if only on this point. The question is, in fact, one of cardinal importance. But it is a pity that, as we have seen, Petzoldt himself was not only unable to cope with this question, but could not even approach it. It does not occur to him either that man’s sensations and ideas can be related in a law-governed manner to the external world. I shall not go as far as to say that Petzoldt could not even approach this question because he has one of those ‘minds that think formally’. Of course, his thinking is distinguished by a strange formalism, but the matter does not end there. Petzoldt’s formal mind, in addition, did not have the proper information. Quite unconsciously, he continued to be under the influence of the idealist theory of knowledge even while he was rebelling against it. And it was only because he remained under its influence that he could maintain the belief that if the world exists not only ‘for us’, but also ‘in itself’, then its being-'in-itself’ is beyond the reach of our external senses. This is just the same belief he chides Parmenides for holding: the belief in the absence of any relation conforming to law between being ‘in itself’ and being ‘for us’. By clinging to this belief, he naturally discerned dualism where in fact there was none. To get rid of this illusory dualism, and lacking knowledge of the materialist theory of cognition, he could think of nothing better than to deny ‘being-in-itself’. And this was tantamount to reconciliation with idealism. The only difference was that one idealist theory of cognition was replaced by another still less satisfactory and still more contradictory. He wanted to move forward, but instead he moved backward, extremely pleased with himself and imagining that his retreat practically solved the most difficult philosophical question ‘once and for all’. All the arguments advanced by Petzoldt in defence of his thesis are constructed on a proposition borrowed from the idealists, viz, that ‘being-in-itself’ cannot be accessible to our external senses. The more often he repeats this proposition, the more clearly revealed is the kinship of ‘modern’ positivism with idealism of the purest water. True, Petzoldt is afraid to admit this kinship, but fear is not a reason, and not even an extenuating circumstance. Idealism, having turned cowardly, has not then ceased to be idealism.
How poorly Petzoldt is acquainted with materialism may be seen, incidentally, from the following passage in his book. While noting that ‘the preservation of spiritual substance only’, which is characteristic of spiritualism, is empirically and logically impossible, he proceeds:
Matters are no better with the corresponding materialist reduction, the elimination of the spiritual substance in favour of the material. To assert that the perception of a colour, a sound, a pain, or the concepts of loyalty, valour, science, war are identical with the process of motion within the brain, that these sensations are one and the same as this motion and not merely caused by it, is just as insufferable as to assert that the world is only an idea, something without extension. (pp 162-63)
Our author would find himself in a real quandary if we were to ask him which materialist exactly and in which work asserted that perception and thought are identical with motion within the brain. True, two pages further he writes that Hobbes ‘explicitly denies spiritual phenomena, as being immaterial’. But that is a very inept reference. Hobbes looked upon spiritual processes as the inner states of matter in motion and, of course, appropriately organised. Anyone who goes to the trouble of reading his books may confirm this for himself. Petzoldt would apparently have been far more justified had he cited the well-known dictum: ‘thought is matter in motion’. But, first of all, this phrase was coined by someone who was by no means an authority on questions of materialist philosophy,  and nothing similar to that assertion will be found in the works of any one of the classical materialists of the seventeenth, eighteenth or nineteenth centuries. Secondly, even this awkward phrase did not suggest the identity of thought and motion but that motion is a necessary and adequate condition of thought.  Thirdly, how does Petzoldt himself not understand that one cannot flay the same ox twice, and that in reproving the materialists for dualism on the ground that they distinguish ‘being-in-itself’ from being-in-perception, he had not the slightest logical ground for accusing them at the same time of making these two concepts identical? Fourth: ‘What need acquaintances to reckon, when you within the mirror writhe and beckon?’ If anyone is guilty of identifying sensation and motion — or more exactly, identifying motion with sensation — it is precisely the modern ‘positivism’ of Mach, Avenarius and Petzoldt. To reproach the materialists with having identified sensation and thought with motion is to thrust on them that ‘doctrine of identity’ whose bankruptcy was so well exposed by Feuerbach, who also demonstrated that this doctrine is a necessary component part of idealist ‘philosophy’.
To cap everything, Petzoldt himself believes it is necessary to include among the materialists those scientists ‘who regard spiritual experiences as the products or physiological functions of material substance, without however identifying them with material phenomena’ (p 165). But if this be true, to what then is ‘reduced’ the reproach hurled at materialism that ‘it eliminates spiritual substance in favour of the material'? Simply to a failure to understand what the materialists are talking about.
Petzoldt corrects himself:
It would be even better to define the essence of the problem by the following delimitation. If the fundamental ideas or concepts which have been developed to explain or describe natural phenomena are applied to explain or describe spiritual processes then we are dealing with materialism. (Ibid)
This correction only makes matters worse. If spiritual phenomena cannot be described or explained by means of the ideas or concepts which were developed to explain or describe natural phenomena, then the dualists are right, since we then have, firstly, natural phenomena and, secondly, spiritual phenomena not included in the first-named. In short, we then have the dualism of nature and the soul or spirit. A fine ‘monism’ this is, that so frequently and so unwittingly lands in the domain of ‘ideas or concepts’ that are typical of dualism! But let us assume that Petzoldt is simply expressing himself badly, and that when he speaks of natural phenomena he is thinking of motion in the proper meaning of the word. The question then arises: which of the prominent representatives of materialism has explained or described spiritual phenomena with the help of ideas or concepts that were developed to explain or describe motion? Not one of the materialists of modern times! All the foremost materialists of these times said that spiritual phenomena and motion are two aspects of the one and the same process taking place in the organised body (belonging, of course, to nature). One may or may not agree with this. However, it cannot but be recognised, without committing the most glaring injustice, that in this there is neither the identification of one series of phenomena with another, nor the admission that it is possible to explain or describe one series of phenomena by the ideas or concepts ‘developed’ to explain or describe another. Petzoldt defines materialism badly because he knows it badly. As a result, it is not surprising that he makes laughable errors every time he takes to criticising it. 
Petzoldt has no better reason either for the reproaches he levels at Spinoza. He says:
Spinoza... understands both substances, not as products of God’s creation, but as aspects of his being. God does not only think, he also has extension; he has not only a soul, but also a body; he is identical with nature, that is, for Spinoza, with the world. This pantheism signifies the lessening and perhaps the complete elimination of the power of the anthropomorphic conception of God, but it leaves untouched the main problem of the theory of cognition. For if to our philosopher matter and spirit are really not two distinct substances, but only attributes of the one and only substance of God, then for our problem this is essentially only a mere renaming of old concepts. We still do not know how material brain processes give rise to immaterial spiritual processes and vice versa, or how relationships conforming to law are established between these aspects which, even according to Spinoza, have nothing in common; and for the elucidation of all this it is a matter of indifference whether they are called substances or only attributes. (p 141)
No, it is not a matter of indifference; far from it. Difference in name is of no significance only where it is not accompanied by difference in the corresponding concept. To Spinoza, the new name means a new concept. In eliminating the doctrine of two substances, Spinoza expelled from the domain of philosophy that animism to which Descartes had paid such heavy tribute, to which every idealist pays equally lavish tribute, and which, in Petzoldt’s opinion (a justifiable one this time), constitutes one of the greatest errors of human thought. Further, it is strange to reproach Spinoza with not having explained how material brain processes give rise to immaterial spiritual processes. Did not the author of Ethics say outright that the second kind of processes are not caused by the first kind, but only attend them. ‘The soul and the body’, said Spinoza, ‘are but one and the same thing, conceived now under the attribute of thought, now under the attribute of extension.’  Take stock of these words of Spinoza and see if there is even an iota of sense left in the question of how spiritual processes are caused by corporeal processes. You see that the question is absolutely devoid of all meaning. The attribute of thought is not caused by the attribute of extension, but is simply the reverse side of ‘one and the same thing’, one and the same process. Petzoldt’s censure of Spinoza is tantamount to blaming this brilliant Jew for not explaining how one and the same process, conceived of from the angle of varying attributes, may present itself quite differently. But Spinoza never undertook this task. The fact that extension and thought are essentially two attributes of one and the same substance was for him an established fact, which explains many other facts, but is not itself subject to explanation. It is remarkable that the same Petzoldt credits Spinoza with eliminating ‘the so-called interaction of body and spirit’. He says that having got rid of this interaction, Spinoza thereby prepared the ground for the latest views (p 141). But surely it must be clear that Spinoza could only have postulated the question of how material brain processes give rise to immaterial spiritual processes if he had recognised the interaction of body and spirit. Petzoldt reproves Spinoza for not tackling this question, and simultaneously praises him for having refuted the interaction of body and spirit. A wonderful power of logic!
Petzoldt avers that ‘already in Spinoza’s works we encounter the idea to which Leibniz later gave the appellation pre-established harmony’ (p 142). As a matter of fact, Spinoza was spurned by the theologians of all countries, to use Lessing’s phrase, ‘like a dead dog’, because he had left no room in his philosophy for a being who could establish ‘harmony’.  Petzoldt calls Spinoza’s teaching on the mutual relationship of thought and extension the doctrine of pre-established harmony:
Thus, two series of completely independent processes flow side by side... When a physical phenomenon recurs, there will recur with it the spiritual phenomenon which previously manifested itself together with it, and vice versa. (p 142)
Well, isn’t it true? Is it a ‘metaphysical’ invention by Spinoza? A man drinks a bottle of vodka: that is a ‘physical phenomenon’. He gets drunk and all sorts of nonsense comes into his head: that is a ‘spiritual phenomenon’. Some days later he drinks another bottle of vodka: again a ‘physical phenomenon’. Once again he gets drunk, and again his head is filled with all kind of nonsense: this again is a ‘spiritual phenomenon’. ‘When a physical phenomenon recurs, there will recur with it the spiritual phenomenon which previously manifested itself together with it.’ Surely everybody knows that? But what do the words ‘and vice versa’ mean which Petzoldt attaches to the sentence I have just quoted? I must confess their meaning is beyond me. It must be that we have to see the example of the drunken man like this: the man gets drunk and the full bottle is found to be empty. Otherwise ‘and vice versa’ is meaningless.  But however that may be, it is a fact that certain relationships conforming to law exist between psychical phenomena on the one hand and physiological phenomena on the other. Petzoldt himself, of course, does not deny this. But he finds that Spinoza explained these relationships badly. Let us agree with him for the time being and ask: are these relationships explained any better in idealist philosophy? Petzoldt will say no. What remains? ‘Modern’ positivism! We turn to ‘modern’ positivism.
Petzoldt contends that the mistake of all philosophical teachings prior to this positivism consisted in the following:
They could not conceive of any other mutual dependence of natural phenomena than that of sequence in time: first A, then B; but not as in geometry: if A, then B. According to the geometrical method, if the sides of a triangle are equal, then the opposite angles are also equal... If attention is directed to this completely general functional dependence of both geometrical and physical determining elements, then it is not difficult to conceive as analogous the relationships between spiritual and bodily phenomena (or determining elements), thereby bridging the gulf separating the two worlds. But Spinoza, although he set forth the basic principles of his main work and proved them, following strictly the model of Euclid’s geometry, and although he weakened the contrast between the two substances, reducing them to the level of two aspects of one and the same substance, nevertheless was very far from the aforesaid analogy. He was unable to think of parallelism between the spiritual and bodily processes in the form of the interrelation between x and y in the equation: y equals f (x), but needed a connective member between the two variable quantities, namely the conception of substance. (pp 142-43)
So there we are: if A, then B; if the sides of a triangle are equal, then the opposite angles are also equal. That is indeed very simple. If a man has drunk a litre of vodka, then he has become intoxicated: which was to be proved. But does it answer the question with which Petzoldt has just been pestering Spinoza? Do we now know — thanks to ‘modern’ positivism — ‘how’ the given relationships conforming to law are established between A and B? Do we now know what determines the reciprocal relationship of spiritual and bodily phenomena? No, we do not. And it is all too clear that if we in turn began to worry Petzoldt with these questions, then he would decline to answer, on the ground that science discovers that phenomena are regulated by laws, but does not explain why there is this conformity to law. And he would be right. However, as the Germans justifiably say, was dem einen recht, ist dem anderen billig.  Here also is a sort of ‘if — then’. If Petzoldt cannot be reproached for having an inclination towards the doctrine of pre-established harmony, then neither can Spinoza; for both of them leave one and the same question unanswered.
The only difference is that Spinoza ‘needed a connective member between the two variable quantities, namely the conception of substance’, and Petzoldt did not. But it is now clear from what has been said that the difference is not at all in Petzoldt’s favour.
In analysing Hume’s views on the relationship of the ‘inner world’ to the external world, Petzoldt thus formulates his own theory on this subject:
Both worlds emerge from indifferent elements in the process of mutual differentiation and interrelationship. And this already indicates that they exist in relations of mutually functional dependence, while at the same time having a common independent root. (p 172)
Whatever these ‘indifferent elements’ may be, the differentiation of which leads, in Petzoldt’s words, to the emergence of the external world on the one hand, and the inner world on the other, one thing is clear: these two worlds have no sooner emerged than a relationship is established between them which is usually referred to as the relationship of the object to the subject. We already know just how badly the ‘new’ positivism explains — or it would be better to say: how much it confuses — the conception of this relationship. Consequently, I shall not enlarge upon it. I will only remark that, here also, our author does not explain to us why certain reciprocal relationships are established between the ‘inner’ world and the ‘external’ world: that is to say, he is guilty — if one can speak of guilt in this case — of doing exactly the same thing he accused Spinoza of doing. However, there is a morsel of truth in the remark cited above. The two worlds really ‘do have a common root’. To the degree that this is correct, it comes nearer to Spinoza’s doctrine that thought and extension are essentially two attributes of one and the same substance. Petzoldt is not in error only when he repeats the materialist doctrine of Spinoza which he has repudiated, albeit presenting that doctrine in an extremely muddled form.
But most interesting of all is the ‘conclusion’ our author draws from Spinoza’s teaching. It is so incredible that I cannot expound its underlying argument in my own words, and must leave that to Petzoldt himself:
This conclusion consists first of all in this: that the souls of two people, A and B, cannot communicate anything to each other and are completely isolated from each other. Only their bodies, in particular the cerebra, are in mutual contact by means of their motions of expression, in particular, the motions of the speech organs. The sounds produced by A set the air in vibrations; the airwaves strike B’s ear-drum, and its vibrations are transferred to the auditory nerve which, in turn, communicates its impulses to the cerebrum. There, all kinds of complicated changes occur, which finally lead to movements of subject B’s organs of speech; and these movements, traversing now the return journey, reach A’s cerebrum. But at no time does any of these manifestations touch the souls of the two subjects. Their cerebra alone carry on the conversation; their souls know nothing about it. (pp 146-47)
One would have to know nothing whatever of Spinoza’s philosophy to believe this. The author of Ethics must, apparently, have foreseen his Petzoldt and tried to anticipate this preposterous ‘conclusion’. Theorem XII of Part II of Spinoza’s main work reads:
Whatever comes to pass on the subject of the idea, which constitutes the human soul, must be perceived by the human soul, or there will necessarily be an idea in the human soul of the said occurrence. That is, if the object of the idea constituting the human soul be a body, nothing can take place in that body without being perceived by the soul. 
After that one may judge how profound is the conclusion reached which has its culminating point in the words: ‘Their cerebra alone carry on the conversation; their souls know nothing about it.’ If Spinoza had taught that ‘brains’ could carry on a conversation about which the ‘soul’ knew nothing, he would have been a dualist and not a monist, and we should again be confronted with the two independent substances, with one of them — the ‘soul’ — having allotted to it all psychical phenomena, while the other — the ‘body’ — would be regarded as incapable of either sensation or thought, in which case it would be beyond all comprehension how such material things as brains could ‘carry on a conversation’. To get out of this difficulty, it would only remain for us to assume that matter can think, that is to say, to go back to the teaching of the same Spinoza for whose refutation there was invented the ‘conclusion’ about conversing ‘brains’ and ‘isolated’ souls.
Petzoldt himself feels that his conclusion is directly opposed to what Spinoza said, and consequently hastens to put things right by the following consideration:
If, in spite of this, simultaneously with the brain processes there occur processes in the soul corresponding to those of the brain — and therefore to one another — the cause of this is that pre-established harmony, that mathematical magical term which, at the proper moment, substitute itself for the missing concept and makes things so different, in the sense of their premises, as soul and body, only aspects of one and the same thing. (p 147)
But I said already that the doctrine of pre-established harmony is being foisted on Spinoza by Petzoldt without the slightest justification. As for love of mathematical magical terms, this is the distinguishing feature of precisely the ‘modern’ positivists. We have seen this from Petzoldt’s example. Was it not he who told us that the mathematical concept of functional dependence enables us to bridge the gulf separating spiritual from bodily phenomena? But there’s the rub: Petzoldt has a flair for putting the blame on someone else. On page 143 of his book, he refers to the concept of functional dependence, claiming that it will help us to ‘bridge’, etc, while on page 147 he accuses Spinoza of having a love for ‘mathematical magical terms’. Willy-nilly, we recall Krylov’s bear advising the monkey to look at itself in the mirror, instead of counting up its acquaintances. 
Someone will tell us, perhaps, that to Petzoldt the ‘mathematical term’ signifies a certain concept, whereas this concept is absent in Spinoza’s teaching, having been replaced by this mathematical term. It is obvious that this is exactly what Petzoldt himself wishes to convey. But this reproach has no more basis than any of the others. First, one may disagree with Spinoza’s doctrine of the two attributes of a single substance, but it is decidedly out of the question to describe this doctrine as lacking in content. Secondly, we have seen that Petzoldt himself, in his theory of the relationship between psychical and physical phenomena, avoids falling into contradictions only when he reproduces Spinoza’s idea, though in a distorted form. Finally — last but not least  — notwithstanding Spinoza’s geometrical method of presentation, he very seldom had recourse to ‘mathematical terms’ in his reasoning, as is known to all who have read his Ethics. Why throw the blame on someone else? I pass over such logical conclusions from Spinoza’s teaching as these:
Souls are isolated both in relation to each other and in relation to the external world. Just as in fact they cannot hear, neither can they see or have any kind of perception of the world around them. (p 147)
We already know that such conclusions may be drawn from Spinoza’s teaching only with the aid of that strange logic which makes itself felt on every page of Petzoldt’s book. But I cannot resist the temptation to point to the following ‘inevitable conclusion from Spinoza’s teaching’. This conclusion winds up the chapter devoted to the author of Ethics, and I should like to leave the reader with a happy memory of this chapter:
I myself am a soul, completely cut off from the external world. What, then, gives me the right to speak at all of a world existing outside myself? Nothing, absolutely nothing. The world may exist — that cannot be denied. It could be, however, that I alone exist in the world, that I myself am this world, a world composed exclusively of ideas coming and going. And even if a world outside myself did exist, there is nothing I could presume regarding its arrangement. I shall never know whether there exist other beings like myself. I know now that those whom I formerly took to be beings like myself are only my ideas. But even if I did know that there were such beings, it would not make things easier for me. I could never really have intercourse with them. It must, therefore, be to me a matter of extreme indifference whether they exist or not. In my world I am alone — the world is my own. (p 148)
As an example of the ‘logical conclusions’ to be drawn from Petzoldt’s thesis, that is not at all bad. And since we are aware that the antinomy between the antithesis and the thesis was resolved in favour of the thesis, the above passage may be described as a caricature by Petzoldt of his own philosophical theory. Painters are often known to paint their own portraits. But as far as I know philosophers have hitherto not drawn caricatures of their own views. Petzoldt is a real innovator in this respect, and therein lies the true originality of his book. It deserves great and sympathetic attention.
Mr P Yushkevich has written his own preface to this book, heading it On the Question of the World Enigma. It is worthwhile saying a few words about this preface.
Mr P Yushkevich finds Petzoldt’s book interesting because it is devoted to ‘one of the fundamental questions of philosophy’, the question of the existence of things independently of us. Generally speaking, he is satisfied with the reply given to this question by Petzoldt; but he thinks it needs some ‘correction’, since without this Petzoldt’s solution ‘does not by any means eliminate all doubts’ (pp 17, 28). We know by now that this is indeed so, even more so; in fact, Petzoldt’s ‘solution’ does not eliminate a single doubt. But why is Mr P Yushkevich not fully satisfied with it? In his book, Petzoldt frequently refers to Protagoras’ proposition: ‘To each man the world is as it appears to him.’  It is in respect of this proposition that Mr P Yushkevich suggests his correction:
If we are to proceed from Protagoras’ principle [he says], it must be taken in the most general and, therefore, the most relative form: to each man the world is as it appears to him at each given moment... A tree to me is not simply green. At such and such a moment it has such and such a shade of green; at another moment — a different shade... If at different moments t1, t2, t3,... tn I have different images of the tree: A1, A2, A3, ... An, and if I do not take their arithmetical mean, do not take their end image A (= ‘the tree is green’), then at which of these images must I stop when I am speaking of the existence of trees outside myself? At none in particular, which means at them all. (pp 17, 18, 19)
From this Mr P Yushkevich draws the justifiable conclusion that absolute relativism devours itself. What then? Mr P Yushkevich says that relativism too has to be regarded from a ‘relativist’ point of view; relativism must restrict itself, otherwise it will degenerate into absurdity. Mr P Yushkevich writes:
Heraclitus taught that one cannot swim in one and the same river twice. One cannot swim in the same river once, taught Cratylus,  elevating his dynamism into a certain absolute. Since everything is fluid, is constantly changing, there is nothing recurring. There is no ‘one and the same thing’, there is only diversity: nothing can be said about anything, since a word is also ‘one and the same’ and when we use a word we are fixing something which recurs, that is to say, which does not exist. A thought, once spoken, is a lie. But this thought, too, being spoken, is a lie — it negates itself. (pp 19-20)
Mr P Yushkevich is speaking the truth here, but it is a truth, incidentally, that was much better expressed by Hegel who said that existence (Dasein) is the first negation of negation. But to state this incontestable truth still does not mean that we have solved the question of things existing independently of ourselves. Mr P Yushkevich is quite right when he says: ‘Extreme relativism coincides with extreme solipsism — a solipsism of the moment, knowing only the one present moment.’ (p 21) More than once we have had occasion to witness how Petzoldt’s illusory positivism leads fatally to solipsism. But what exactly is the correction which, in Mr P Yushkevich’s opinion, could lead us out of the blind alley of solipsism?
He asserts that the question of the existence of the objective world, independent of our perceptions, presupposes the existence of ‘some fairly significant community of organisation’. He repeats Protagoras’ phrase: man is the measure of all things, and goes on:
By the same right, we could say that ‘a worm is the measure of all things’ — ‘the amoeba is the measure of all things’, and so on. If we do single out man in this connection, it is only because he is a measure which is conscious of being a measure. This consciousness is the product of the social elaboration of experience, presupposing a high degree of agreement between human organisations. ‘Social man is the measure of things.’ Only this social man, who has recognised himself to be a measure, later endows each separate personality, every living creature, with its special individual measure of being. (pp 23-24)
That is truly a brilliantly simple solution. In order to get out of the blind alley of solipsism, all we have to do is to imagine that we are not in this dreary alley, but in the pleasant company of human beings like ourselves. All our troubles have disappeared as with the waving of a magic wand. There is but one regret: we still do not know by what logical right we give such freedom to our imagination. But if we do not insist upon this painful question, everything will go swimmingly:
Confronting us [Mr P Yushkevich reassures us] are most diverse individual pictures of the world, some similar, some different; before us also is the collective system of experience, the social image of the world, derived from these similarities. This social picture of the world is, of course, not an ‘absolute’ one. It changes in accordance with the acquisitions of knowledge, to the extent that the constantly widening collective experience discovers new diversities for us, but also new and more profound similarities between the diverse individual experiences. But no matter how far from the absolute the social human conception of the world is, in our eyes it has its special importance alongside the individual images of the world. It is precisely to this that we refer when we speak of the ‘real’, the ‘independent’, the ‘objective’, etc, world. (pp 24-25)
This is, perhaps, a slight improvement on absolute relativism. But what is new in Mr Yushkevich’s ‘correction'? Absolutely nothing. It is an old idealist tune: that which exists in the minds of all people is objective. But to exist in the minds of all people is to exist in a conception common to all. And if our ‘picture of the world’ is objective only because it exists in the minds of all people, we are idealists, regarding the world as a conception. Meanwhile, Petzoldt, with whom Mr P Yushkevich is in full agreement, apart from the exception indicated, categorically declares that ‘the doctrine of the world as a conception’ is a ‘colossal absurdity’ (p 146). Try and understand that! Amazing compliments these gentlemen of ‘modern’ positivism pay one another.
A word or two more. Mr P Yushkevich admits that, if man is the measure of things, then a worm is a measure of things too, an amoeba is a measure of things, and so on. Man is singled out ‘by us’ in this respect ‘only because he is a measure which is conscious of being a measure’. We have to suppose that neither the worm nor the amoeba are in fact conscious of themselves as measures, and do not study philosophy. But although in this respect they do not resemble man, a fact is still a fact and is admitted as such even by Mr P Yushkevich: the ‘worm’ does not have the same ‘picture of the world’ as the ‘amoeba’, and the ‘amoeba’ has not the same picture that man has. How does this come about? It is because the material organisation of man does not resemble the material organisation of the other two ‘measures of things’. What does this mean? It means that consciousness (’the picture of the world’ peculiar to each particular ‘measure of things’) is determined by being (the material organisation of that ‘measure’). And that is pure materialism which our ‘modern’ positivists refuse to have anything to do with. Against this, of course, it may be objected, as is done in no uncertain fashion by all adversaries of materialism, that the amoeba and the worm, as well as the material organisation of one and the other, are nothing more than our conceptions. But if this is true, where does logic come in? For then it will turn out that to explain the character of ‘our picture of the world’, that is to say, the totality of ‘our’ conceptions systematised in some way or other, we and Mr Yushkevich are referring to the difference between all of this picture, on the one hand, and the ‘picture of the world’ as seen by some of its component parts — in this instance, the worm and the amoeba. Our imagination is first of all our imagination, and then the imagination of the picture of the world peculiar to the worm. In other words, we imagine to ourselves an image peculiar to some of our imaginations — and this is what constitutes ‘our entire scientific method’, and everything that we can oppose to materialism reduces itself to this ‘scientific method’. It isn’t very much! But Petzoldt imagines that the ‘world-outlook’ elaborated by this method, absurd in the true sense of the word, may perhaps be recognised as ‘final in all its main features’. To be sure, he has thought of a fine ending to the history of philosophical thought! 
However, I repeat: Petzoldt’s book is evidently assured of great success among some circles of our reading public. In it is enunciated the very miserable philosophy of cowardly idealism. But this miserable philosophy is well suited to our miserable times. Hegel justly remarked that any philosophy is but the ideological expression of its time. The Russian people has expressed, if you like, that same thought, but in a more general form by saying: ‘Senka has the cap that fits him!’
Notes are by Plekhanov, except those by the Moscow editors of this edition of the work, which are noted ‘Editor’, or the MIA, which are suitably noted.
1. Wilhelm Schuppe (1836-1913) — German philosopher, subjective idealist; Ernst Mach (1838-1916) — Austrian physicist and idealist philosopher, one of the founders of empiric-criticism; Richard Avenarius (1843-1896) — German idealist philosopher, formulated the basic principles of empiric-criticism — Editor.
2. Alexander Alexandrovich Bogdanov (Malinovsky) (1873-1928) — Russian Social-Democrat, philosopher and sociologist, tried to create his own philosophical system — empiriomonism (a variant of Machism); N Valentinov (Nikolai Vladislavovich Volsky) (1879-?) — Social-Democrat, Menshevik and Machist philosopher; Pavel Solomonovich Yushkevich (1873-1945) — Russian Social-Democrat, revisionist of Marxist philosophy, which he sought to replace with empirio-symbolism, a variety of Machism — Editor.
3. Heraclitus of Ephesus (c 530-470 BC) — Greek materialist philosopher, one of the founders of dialectics; Parmenides (late sixth century-early fifth century BC) — Greek philosopher, chief representative of the Eleatic school — Editor.
4. Protagoras of Abdera (481-411 BC) — Greek sophist philosopher, ideologist of slave-holding democracy — Editor.
5. David Hume (1711-1776) — Scottish philosopher, subjective idealist; Thomas Hobbes (1588-1679) — English materialist philosopher — Editor.
6. I call Petzoldt’s positivism modern because he severs connection with the old positivism of Auguste Comte and Mill. ‘Alongside of the Kant variety of idealism’, we read on page 195 of the book under review, ‘there is also positive idealism. It knows no a priori conditions of experience (Comte, Mill) but, as pure phenomenalism, is as untenable as the first.’ I earnestly beg the reader to note the reason given by Petzoldt for the rupture of the ‘modern’ positivism with the old. [Auguste Comte (1798-1857) — French philosopher and sociologist, founder of positivism; John Stuart Mill (1806-1873) — English bourgeois economist and positivist philosopher — Editor.]
7. Literally ‘One, two three; speed is not sorcery!’ It would be better translated as ‘One, two, three; speed is no sleight of hand!’ or ‘Nothing up my sleeve!’, that is, ‘Because I can do it quickly doesn’t mean there’s trickery involved.’ Plekhanov was being his usual sarcastic self here. Thanks to Chris Gray for the explanation — MIA.
8. Indeed, in his attempt to solve the antinomy we are discussing he does not pass beyond the limits of Schuppe’s well-known, purely idealist principle: ‘Kein Gegenstand ausserhalb des Bewusstseins.’ [’there is no object outside of consciousness.’]
9. ‘If, in this way, Kant does not break with the unnecessary duality of the world into the thing-in-itself and phenomenon’, says Petzoldt, ‘if he even goes backward in comparison with his predecessors... [etc].’ (Page 188 of the book under review.)
10. Poprishchin — a character from Gogol’s Notes of a Madman — Editor. [Poprishchin is a minor civil servant who slowly goes insane and is committed to an asylum — MIA.]
11. ‘Das Ding ist hiernach für sich, und auch für ein anderes, ein gedoppeltes verschiedenes Sein; aber es ist auch Eins.’ [’the Thing is, hence for itself and also for another, a Being that has difference of a dual kind. But it is also one.'] (Hegel, Phänomenologie des Geistes (Bamberg and Würzburg, 1807), p 51) See my remark above on Petzoldt’s pluralism.
12. To be just, I should mention, however, that even materialists have sometimes not refused to repeat idealist phrases about the unknowability of things-in-themselves. Holbach, for instance, was sometimes not innocent of this. But what was simply inconsistency on the part of materialists, was the foundation of the entire idealist gnosiology. Quite a big difference. Let me add that the difference between idealist gnosiology and the materialist theory of knowledge was apparent already in ancient philosophy. W Windelband, in elucidating the ‘main distinction’ between Plato and Democritus in respect to theory and knowledge, says: ‘The last-named also demanded, together with knowledge gained through perception (σκοτίη γνωμη) understood and evaluated in Protagoras’ sense, also true knowledge (γνησίη γνωμη) obtained by thinking; but he believed that one could be deduced from the other; he established a difference between them only of degree, but not in essence. Thus by thinking, operating with concepts... he found, not a new incorporeal world, but only the fundamental element of the same corporeal world — the atom.’ (W Windelband, Plato (St Petersburg, 1904), p 84, footnote) [Paul Henri Holbach (1723-1789) — French materialist philosopher, atheist; Plato (427-347 BC) — Greek philosopher, objective idealist; Democritus (c460-370 BC) — Greek materialist philosopher — Editor.]
13. Plekhanov apparently has in mind the French sensualist Cabanis (1757-1808) who reduced all mental phenomena to physiological ones and maintained that the brain secretes thought as the liver does bile. This proposition was repeatedly criticised and in fact became a ‘celebrated phrase’. Cabanis was a precursor of the vulgar materialists in Germany of the 1850s, Büchner, Vogt and Moleschott, who repeated in particular this proposition of his — Editor.
14. Regarding a similar expression of Vogt’s, ‘the brain secretes thought as the kidneys secrete urine’, even Lange, who was never kindly disposed towards the materialists, remarked: ‘Es ist bei den zahlreichen Erörterungen von Vogts berühmtem Urin-Vergleich wohl klar genug geworden, dass man nicht den “Gedanken” als ein besonderes Produkt neben den stofflichen Vorgängen ansehen kann, sondern dass eben der subjektive Zustand des empfindenden Individuums zugleich für die äussere Beobachtung ein objektiver, eine Molecularbewegung ist.’ ['Vogt’s much discussed comparison of thought with urine clearly reveals that “thought” cannot be regarded as a special product on a level with material processes, but that the subjective state of the perceiving individual is at the same time objective for external observation, is molecular movement.] (FA Lange, Geschichte des Materialismus und Kritik seiner Bedeutung in der Gegenwart, Volume 2 (seventh edition, Leipzig, 1902), p 374) True, in other parts of his work Lange writes as though he never even suspected the possibility of such a remark. But that has to do with his logic, which we are not discussing at the moment. [Friedrich Albert Lange (1828- 1875) — German philosopher, neo-Kantian; Karl Vogt (1817-1895) — German naturalist, vulgar materialist — Editor.]
15. I may be told that this very concept of matter must be changed radically in view of the striking discoveries in physics during recent years. There is a point there. But not one of these discoveries vitiates the definition of matter according to which matter is that (in ‘itself’ existing) which directly or indirectly acts, or in certain circumstances can act, on our external senses. That is good enough for me at the moment.
16. Spinoza, Ethics (St Petersburg), 1894, p 121. [Baruch (Benedict) Spinoza (1632-1677) — Dutch materialist philosopher, rationalist, atheist; René Descartes (1596-1650) — French deist philosopher, mathematician and naturalist — Editor.]
17. Theologians were not satisfied, and could not be, with Spinoza’s use of the word ‘God’, since by this word he meant Nature. He said so: ‘God or Nature’ ('Deus sive natura’). From the point of view of terminology, it was of course incorrect, but that is another question which does not concern us here.
18. The influence of the physical condition upon the physiological processes is often spoken about. Nowadays, the medical profession dilate much and readily on this influence. I think that the facts prompting this idea are often quite correctly indicated. But they are altogether wrongly explained. Those who talk much of the influence of the ‘psychical’ upon the ‘physical’ forget that each particular psychical condition is only one side of the process, the other side being physiological, or to be more accurate, a whole combination of physiological phenomena in the proper meaning of the term. When we say that a particular psychical condition has influenced in a certain way the physiological functions of a particular organism, we have to understand that this influence we speak of was caused, strictly speaking, by those phenomena (which are also purely physiological) the subjective side of which constitutes this psychical condition. If it were otherwise, if this or that psychical conditions could serve as the real cause of physiological phenomena, we should have to renounce the law of the conservation of energy. This has already been adequately dealt with by FA Lange in his Geschichte des Materialismus, Volume 2, p 370 et seq. See also note 39 on pages 440-42 of the same volume. True, Ostwald’s pupils would revolt against my remark concerning the law of the conservation of energy, but I cannot start wrangling with them here. I hope soon to devote a special article to analysing Ostwald’s theory of knowledge. [Wilhelm Friedrich Ostwald (1853-1932) — German chemist and idealist philosopher; exponent of energism, a variety of Machism — Editor.]
19. What is right for one, is right for another — Editor.
20. Ethics, p 66, Spinoza’s italics. It would be useful to contrast this with Theorem XIV in the same Part: ‘The human mind is capable of perceiving a great number of things, and is so in proportion as its body is capable of receiving a great number of impressions. — Proof: The human body (by Postulations III and VI) is affected in very many ways by external bodies, and is capable in very many ways of affecting external bodies. But (Theorem XII in the same Part) the human mind must perceive all that takes place in the human body; the human mind is, therefore, capable of perceiving a great number of things, and is so in proportion, etc — which was to be proved.’ (Ibid, p 75)
21. A reference to Krylov’s tale The Mirror and the Monkey — MIA.
22. These words are in English in the original — Editor.
23. This proposition of Protagoras’ is interpreted by Petzoldt in the sense of extreme subjectivism, even though the latest historians of ancient philosophy are advancing arguments which cast doubt on the correctness of such an interpretation. (See, for example, Théodore Gomperz, Les penseurs de la Grèce. Histoire de la philosophie antique (Lausanne), pp 464-501, especially pp 483 et seq). Mr P Yushkevich says nothing about Petzoldt’s views on Protagoras; evidently he agrees with them.
24. Cratylus (fifth century BC) — Greek idealist philosopher — Editor.
25. Mr Yushkevich’s ‘worm’ and ‘amoeba’ remind me of the question once put by FA Lange: ‘If a worm, a beetle, a man, and an angel look at a tree, do we have five trees?’ He replied that we should have, in all probability, four very distinct conceptions of the tree, but that all four of these would relate to one and the same object (Geschichte des Materialismus, Volume 2, p 102). Lange was right, although it cannot be said that his correct reply could have been very well substantiated with the aid of his (Kantian) theory of cognition. What will Mr Yushkevich reply to this question? How many trees will he have? I suppose he will have as many as Petzoldt would have got; we already know that Petzoldt aspires towards monism but arrives at pluralism. In passing I shall add this: if the tree ‘in itself’ does not exist, whereas the worm, the beetle, the man and the angel have simultaneous, though distinct impressions of it, we have a highly interesting case of ‘pre-established harmony’.