The fundamental premises of the theory of knowledge of Mach and Avenarius are frankly, simply and clearly expounded by them in their early philosophical works. To these works we shall now turn, postponing for later treatment an examination of the corrections and emendations subsequently made by these writers.
"The task of science,” Mach wrote in 1872, “can only be: 1. To determine the laws of connection of ideas (Psychology). 2. To discover the laws of connection of sensations (Physics). 3. To explain the laws of connection between sensations and ideas (Psycho-physics)." This is quite clear.
The subject matter of physics is the connection between sensations and not between things or bodies, of which our sensations are the image. And in 1883, in his Mechanics, Mach repeats the same thought: “Sensations are not ’symbols of things.’ The ’thing’ is rather a mental symbol for a complex of sensations of relative stability. Not the things (bodies) but colours, sounds, pressures, spaces, times (what we usually call sensations) are the real elements of the world.”
About this word “elements,” the fruit of twelve years of “reflection,” we shall speak later. At present let us note that Mach explicitly states here that things or bodies are complexes of sensations, and that he quite clearly sets up his own philosophical point of view against the opposite theory which holds that sensations are “symbols” of things (it would be more correct to say images or reflections of things). The latter theory is philosophical materialism. For instance, the materialist Frederick Engels—the not unknown collaborator of Marx and a founder of Marxism—constantly and without exception speaks in his works of things and their mental pictures or images (Gedanken-Abbilder), and it is obvious that these mental images arise exclusively from sensations. It would seem that this fundamental standpoint of the “philosophy of Marxism” ought to be known to everyone who speaks of it, and especially to anyone who comes out in print in the name of this philosophy. But because of the extraordinary confusion which our Machians have introduced, it becomes necessary to repeat what is generally known. We turn to the first section of Anti-Dühring and read: “. . . things and their mental images . . . “; or to the first section of the philosophical part, which reads: “But whence does thought obtain these principles [i.e., the fundamental principles of all knowledge]? From itself? No . . . these forms can never be created and derived by thought out of itself, but only from the external world . . . the principles are not the starting point of the investigation [as Dühring who would be a materialist, but cannot consistently adhere to materialism, holds], but its final result; they are not applied to nature and human history, but abstracted from them; it is not nature and the realm of humanity which conform to these principles, but the principles are only valid in so far as they are in conformity with nature and history. That is the only materialistic conception of the matter, and Herr Dühring’s contrary conception is idealistic, makes things stand completely on their heads, and fashions the real world out of ideas” (ibid., p. 21). Engels, we repeat, applies this “only materialistic conception” everywhere and without exception, relentlessly attacking Dühring for the least deviation from materialism to idealism. Anybody who reads Anti-Dühring and Ludwig Feuerbach with the slightest care will find scores of instances when Engels speaks of things and their reflections in the human brain, in our consciousness, thought, etc. Engels does not say that sensations or ideas are “symbols” of things, for consistent materialism must here use “image,” picture, or reflection instead of “symbol,” as we shall show in detail in the proper place. But the question here is not of this or that formulation of materialism, but of the opposition of materialism to idealism, of the difference between the two fundamental lines in philosophy. Are we to proceed from things to sensation and thought? Or are we to proceed from thought and sensation to things? The first line, i.e., the materialist line, is adopted by Engels. The second line, i.e., the idealist line, is adopted by Mach. No evasions, no sophisms (a multitude of which we shall yet encounter) can remove the clear and indisputable fact that Ernst Mach’s doctrine that things are complexes of sensations is subjective idealism and a simple rehash of Berkeleianism. If bodies are “complexes of sensations,” as Mach says, or “combinations of sensations,” as Berkeley said, it inevitably follows that the whole world is but my idea. Starting from such a premise it is impossible to arrive at the existence of other people besides oneself: it is the purest solipsism. Much as Mach, Avenarius, Petzoldt and the others may abjure solipsism, they cannot in fact escape solipsism without falling into howling logical absurdities. To make this fundamental element of the philosophy of Machism still clearer, we shall give a few additional quotations from Mach’s works. Here is a sample from the Analyse der Empfindungen ; (I quote from Kotlyar’s Russian translation, published by Skirmunt, Moscow, 1907):
"We see a body with a point S. If we touch S, that is, bring it into contact with our body, we receive a prick. We can see S without feeling the prick. But as soon as we feel the prick we find S on the skin. Thus, the visible point is a permanent nucleus, to which, according to circumstances, the prick is attached as something accidental. By frequent repetitions of analogous occurrences we finally habituate ourselves to regard all properties of bodies as ’effects’ which proceed from permanent nuclei and are conveyed to the self through the medium of the body; which effects we call sensations . . .” (p. 20).
In other words, people “habituate” themselves to adopt the standpoint of materialism, to regard sensations as the result of the action of bodies, things, nature on our sense organs. This “habit,” so noxious to the philosophical idealists (a habit acquired by all mankind and all natural science!), is not at all to the liking of Mach, and he proceeds to destroy it:
“ . . . Thereby, however, these nuclei are deprived of their entire sensible content and are converted into naked abstract symbols . . . . ”
An old song, most worthy Professor! This is a literal repetition of Berkeley who said that matter is a naked abstract symbol. But it is Ernst Mach, in fact, who goes naked, for if he does not admit that the “sensible content” is an objective reality, existing independently of us, there remains only a “naked abstract” I, an I infallibly written with a capital letter and italicised, equal to “the insane piano, which imagined that it was the sole existing thing in this world.” If the “sensible content” of our sensations is not the external world then nothing exists save this naked I engaged in empty “philosophical” acrobatics. A stupid and fruitless occupation!
“ . . . It is then correct that the world consists only of our sensations. In which case we have knowledge only of sensations, and the assumption of those nuclei, and of their interaction, from which alone sensations proceed, turns out to be quite idle and superfluous. Such a view can only appeal to half-hearted realism or half-hearted criticism.”
We have quoted the sixth paragraph of Mach’s “anti-metaphysical observations” in full. It is a sheer plagiarism on Berkeley. Not a single idea, not a glimmer of thought, except that “we sense only our sensations.” From which there is only one possible inference, namely, that the “world consists only of my sensations.” The word “our” employed by Mach instead of “my” is employed illegitimately. By this word alone Mach betrays that “half-heartedness” of which he accuses others. For if the “assumption” of the existence of the external world is “idle,” if the assumption that the needle exists independently of me and that an interaction takes place between my body and the point of the needle is really “idle and superfluous,” then primarily the “assumption” of the existence of other people is idle and superfluous. Only I exist, and all other people, as well as the external world, come under the category of idle “nuclei.” Holding this point of view one cannot speak of “our” sensations; and when Mach does speak of them, it is only a betrayal of his own amazing half-heartedness. It only proves that his philosophy is a jumble of idle and empty words in which their author himself does not believe.
Here is a particularly graphic example of Mach’s half heartedness and confusion. In § 6 of Chapter XI of the Analysis of Sensations we read: “If I imagine that while I am experiencing sensations, I or someone else could observe my brain with all possible physical and chemical appliances, it would be possible to ascertain with what processes of the organism particular sensations are connected . . . ” (p. 197).
Very well! This means, then, that our sensations are connected with definite processes, which take place in the organism in general, and in our brain in particular? Yes, Mach very definitely makes this “assumption"—it would be quite a task not to make it from the standpoint of natural science! But is not this the very “assumption” of those very same “nuclei and their interaction” which our philosopher declared to be idle and superfluous? We are told that bodies are complexes of sensations; to go beyond that, Mach assures us, to regard sensations as a product of the action of bodies upon our sense-organs, is metaphysics, an idle and superfluous assumption, etc., à la Berkeley. But the brain is a body. Consequently, the brain also is no more than a complex of sensations. It follows, then, that with the help of a complex of sensations I (and I also am nothing but a complex of sensations) sense complexes of sensations. A delightful philosophy! First sensations are declared to be “the real elements of the world"; on this an “original” Berkeleianism is erected—and then the very opposite view is smuggled in, viz., that sensations are connected with definite processes in the organism. Are not these “processes” connected with an exchange of matter between the “organism” and the external world? Could this exchange of matter take place if the sensations of the particular organism did not give it an objectively correct idea of this external world?
Mach does not ask himself such embarrassing questions when he mechanically jumbles fragments of Berkeleianism with the views of natural science, which instinctively adheres to the materialist theory of knowledge. . . . In the same paragraph Mach writes: “It is sometimes also asked whether (inorganic) ‘matter’ experiences sensation....” Does this mean that there is no doubt that organic matter experiences sensation? Does this mean that sensation is not something primary but that it is one of the properties of matter? Mach skips over all the absurdities of Berkeleianism! . . . “The question,” he avers, “is natural enough, if we proceed from the current widespread physical notions, according to which matter is the immediate and indisputably given reality, out of which everything, inorganic and organic, is constructed....” Let us bear in mind this truly valuable admission of Mach’s that the current widespread physical notions regard matter as the immediate reality, and that only one variety of this reality (organic matter) possesses the well-defined property of sensation. . . . Mach continues: “Then, indeed, sensation must suddenly arise somewhere in this structure consisting of matter, or else have previously been present in the foundation. From our standpoint the question is a false one. For us matter is not what is primarily given. Rather, what is primarily given are the elements (which in a certain familiar relation are designated as sensations). . . . ”
What is primarily given, then, are sensations, although they are “connected” only with definite processes in organic matter! And while uttering such absurdities Mach wants to blame materialism ("the current widespread physical notion") for leaving unanswered the question whence sensation “arises.” This is a sample of the “refutation” of materialism by the fideists and their hangers-on. Does any other philosophical standpoint “solve” a problem before enough data for its solution has been collected? Does not Mach himself say in the very same paragraph: “So long as this problem (how far sensation extends in the organic world) has not been solved even in a single special case, no answer to the question is possible.”
The difference between materialism and “Machism” in this particular question thus consists in the following. Materialism, in full agreement with natural science, takes matter as primary and regards consciousness, thought, sensation as secondary, because in its well-defined form sensation is associated only with the higher forms of matter (organic matter), while “in the foundation of the structure of matter” one can only surmise the existence of a faculty akin to sensation. Such, for example, is the supposition of the well-known German scientist Ernst Haeckel, the English biologist Lloyd Morgan and others, not to speak of Diderot’s conjecture mentioned above. Machism holds to the opposite, the idealist point of view, and at once lands into an absurdity: since, in the first place, sensation is taken as primary, in spite of the fact that it is associated only with definite processes in matter organised in a definite way; and since, in the second place, the basic premise that bodies are complexes of sensations is violated by the assumption of the existence of other living beings and, in general, of other “complexes” besides the given great I.
The word “element,” which many naïve people (as we shall see) take to be some sort of a new discovery, in reality only obscures the question, for it is a meaningless term which creates the false impression that a solution or a step forward has been achieved. This impression is a false one, because there still remains to be investigated and reinvestigated how matter, apparently entirely devoid of sensation, is related to matter which, though composed of the same atoms (or electrons), is yet endowed with a well-defined faculty of sensation. Materialism clearly formulates the as yet unsolved problem and thereby stimulates the attempt to solve it, to undertake further experimental investigation. Machism, which is a species of muddled idealism, befogs the issue and side tracks it by means of the futile verbal trick, “element.”
Here is a passage from Mach’s latest, comprehensive and conclusive philosophical work that clearly betrays the falsity of this idealist trick. In his Knowledge and Error we read: “While there is no difficulty in constructing (aufzubauen) every physical experience out of sensations, i.e., psychical elements, it is impossible to imagine (ist keine Möglichkeit abzusehen) how any psychical experience can be composed (darstellen) of the elements employed in modern physics, i.e., mass and motion (in their rigidity—Starrheit—which is serviceable only for this special science).”
Of the rigidity of the conceptions of many modern scientists and of their metaphysical (in the Marxist sense of the term, i.e., anti-dialectical) views, Engels speaks repeatedly and very precisely. We shall see later that it was just on this point that Mach went astray, because he did not understand or did not know the relation between relativism and dialectics. But this is not what concerns us here. It is important for us here to note how glaringly Mach’s idealism emerges, in spite of the confused—ostensibly new—terminology. There is no difficulty, you see, in constructing any physical element out of sensations, i.e., psychical elements! Oh yes, such constructions, of course, are not difficult, for they are purely verbal constructions, shallow scholasticism, serving as a loophole for fideism. It is not surprising after this that Mach dedicates his works to the immanentists; it is not surprising that the immanentists, who profess the most reactionary kind of philosophical idealism, welcome Mach with open arms. The “recent positivism” of Ernst Mach was only about two hundred years too late. Berkeley had already sufficiently shown that “out of sensations, i.e., psychical elements,” nothing can be “built” except solipsism. As regards materialism, against which Mach here, too, sets up his own views, without frankly and explicitly naming the “enemy,” we have already seen in the case of Diderot what the real views of the materialists are. These views do not consist in deriving sensation from the movement of matter or in reducing sensation to the movement of matter, but in recognising sensation as one of the properties of matter in motion. On this question Engels shared the standpoint of Diderot. Engels dissociated himself from the “vulgar” materialists, Vogt, Büchner and Moleschott, for the very reason, among others, that they erred in believing that the brain secretes thought in the same way as the liver secretes bile. But Mach, who constantly sets up his views in opposition to materialism, ignores, of course, all the great materialists—Diderot, Feuerbach, Marx and Engels—just as all other official professors of official philosophy do.
In order to characterise Avenarius’ earliest and basic view, let us take his first independent philosophical work, Philosophy as a Conception of the World According to the Principle of the Minimum Expenditure of Effort. Prolegomena to a Critique of Pure Experience, which appeared in 1876. Bogdanov in his Empirio-Monism (Bk. I, 2nd ed., 1905, p. 9, note) says that “in the development of Mach’s views, the starting point was philosophical idealism, while a realistic tinge was characteristic of Avenarius from the very beginning.” Bogdanov said so because he believed what Mach said (see Analysis of Sensations, Russian translation, p. 288). Bogdanov should not have believed Mach, and his assertion is diametrically opposed to the truth. On the contrary, Avenarius’ idealism emerges so clearly in his work of 1876 that Avenarius himself in 1891 was obliged to admit it. In the introduction to The Human Concept of the World Avenarius says: “He who has read my first systematic work, Philosophie, etc., will at once have presumed that I would have attempted to treat the problems of a criticism of pure experience from the ‘idealist’ standpoint” (Der menschliche Weltbegriff, 1891, Vorwort, S. ix [The Human Concept of the World, 1891, Foreword, p. ix]), but “the sterility of philosophical idealism compelled me to doubt the correctness of my previous path” (p. x). This idealist starting point of Avenarius’ is universally acknowledged in philosophical literature. Of the French writers I shall refer to Cauwelaert, who says that Avenarius’ philosophical standpoint in the Prolegomena is “monistic idealism.” Of the German writers, I shall name Rudolf Willy, Avenarius’ disciple, who says that “Avenarius in his youth—and particularly in his work of 1876—was totally under the spell (ganz im Banne) of so-called epistemological idealism.”
And, indeed, it would be ridiculous to deny the idealism in Avenarius’ Prolegomena, where he explicitly states that “only sensation can be thought of as the existing” (pp. 10 and 65 of the second German edition; all italics in quotations are ours). This is how Avenarius himself presents the contents of § 116 of his work. Here is the paragraph in full: “We have recognised that the existing (das Seiende) is substance endowed with sensation; the substance falls away [it is “more economical,” don’t you see, there is “a lesser expenditure of effort” in thinking that there is no “substance” and that no external world exists!], sensation remains; we must then regard the existing as sensation, at the basis of which there is nothing which does not possess sensation (nichts Empfindungsloses).”
Sensation, then, exists without “substance,” i.e., thought exists without brain! Are there really philosophers capable of defending this brainless philosophy? There are! Professor Richard Avenarius is one of them. And we must pause for a while to consider this defence, difficult though it be for a normal person to take it seriously. Here, in §§ 89 and 90 of this same work, is Avenarius’ argument:
". . . The proposition that motion produces sensation is based on apparent experience only. This experience, which includes the act of perception, consists, presumably, in the fact that sensation is generated in a certain kind of substance (brain) as a result of transmitted motion (excitation) and with the help of other material conditions (e.g., blood). However—apart from the fact that such generation has never itself (selbst) been observed—in order to construct the supposed experience, as an experience which is real in all its component parts, empirical proof, at least, is required to show that sensation, which assumedly is caused in a certain substance by transmitted motion, did not already exist in that substance in one way or another; so that the appearance of sensation cannot be conceived of in any other way than as a creative act on the part of the transmitted motion. Thus only by proving that where a sensation now appears there was none previously, not even a minimal one, would it be possible to establish a fact which, denoting as it does some act of creation, contradicts all the rest of experience and radically changes all the rest of our conception of nature (Naturanschauung). But such proof is not furnished by any experience, and cannot be furnished by any experience; on the contrary, the notion of a state of a substance totally devoid of sensation which subsequently begins to experience sensation is only a hypothesis. But this hypothesis merely complicates and obscures our understanding instead of simplifying and clarifying it.
"Should the so-called experience, viz., that the sensation is caused by a transmitted motion in a substance that begins to perceive from this moment, prove upon closer examination to be only apparent, there still remains sufficient material in the content of the experience to ascertain at least the relative origin of sensation from conditions of motion, namely, to ascertain that the sensation which is present, although latent or minimal, or for some other reason not manifest to the consciousness, becomes, owing to transmitted motion, released or enhanced or made manifest to the consciousness. However, even this bit of the remaining content of experience is only an appearance. Were we even by an ideal observation to trace the motion proceeding from the moving substance A, transmitted through a series of intermediate centres and reaching the substance B, which is endowed with sensation, we should at best find that sensation in substance B is developed or becomes enhanced simultaneously with the reception of the incoming motion—but we should not find that this occurred as a consequence of the motion. . . .”
We have purposely quoted this refutation of materialism by Avenarius in full, in order that the reader may see to what truly pitiful sophistries “recent” empirio-critical philosophy resorts. We shall compare with the argument of the idealist Avenarius the materialist argument of—Bogdanov, if only to punish Bogdanov for his betrayal of materialism!
In long bygone days, fully nine years ago, when Bogdanov was half “a natural-historical materialist” (that is, an adherent of the materialist theory of knowledge, to which the overwhelming majority of contemporary scientists instinctively hold), when he was only half led astray by the muddled Ostwald, he wrote: “From ancient times to the present day, descriptive psychology has adhered to the classification of the facts of consciousness into three categories: the domain of sensations and ideas, the domain of emotions and the domain of impulses. . . . To the first category belong the images of phenomena of the outer or inner world, as taken by themselves in consciousness. . . . Such an image is called a ‘sensation’ if it is directly produced through the sense-organs by its corresponding external phenomenon.” And a little farther on he says: “Sensation . . . arises in consciousness as a result of a certain impulse from the external environment transmitted by the external sense-organs” (p. 222). And further: “Sensation is the foundation of mental life; it is its immediate connection with the external world” (p. 240). “At each step in the process of sensation a transformation of the energy of external excitation into a state of consciousness takes place” (p. 133). And even in 1905 when with the gracious assistance of Ostwald and Mach Bogdanov had already abandoned the materialist standpoint in philosophy for the idealist standpoint, he wrote (from forgetfulness!) in his Empirio-Monism : “As is known, the energy of external excitation, transformed at the nerve-ends into a ‘telegraphic’ form of nerve current (still insufficiently investigated but devoid of all mysticism), first reaches the neurons that are located in the so-called ‘lower’ centres—ganglial, cerebro-spinal, subcortical, etc.” (Bk. I, 2nd ed., 1905, p. 118.)
For every scientist who has not been led astray by professorial philosophy, as well as for every materialist, sensation is indeed the direct connection between consciousness and the external world; it is the transformation of the energy of external excitation into a state of consciousness. This transformation has been, and is, observed by each of us a million times on every hand. The sophism of idealist philosophy consists in the fact that it regards sensation as being not the connection between consciousness and the external world, but a fence, a wall, separating consciousness from the external world—not an image of the external phenomenon corresponding to the sensation, but as the “sole entity.” Avenarius gave but a slightly changed form to this old sophism, which had been already worn threadbare by Bishop Berkeley. Since we do not yet know all the conditions of the connection we are constantly observing between sensation and matter organised in a definite way, let us therefore acknowledge the existence of sensation alone—that is what the sophism of Avenarius reduces itself to.
To conclude our description of the fundamental idealist premises of empirio-criticism, we shall briefly refer to the English and French representatives of this philosophical trend. Mach explicitly says of Karl Pearson, the Englishman, that he (Mach) is “in agreement with his epistemological (erkenntniskritischen) views on all essential points” (Mechanik, ed. previously cited, p. ix). Pearson in turn agrees with Mach. For Pearson “real things” are “sense-impressions.” He declares the recognition of things outside the boundaries of sense impressions to be metaphysics. Pearson fights materialism with great determination (although he does not know Feuerbach, or Marx and Engels); his arguments do not differ from those analysed above. However, the desire to masquerade as a materialist is so foreign to Pearson (that is a specialty of the Russian Machians), Pearson is so—incautious, that he invents no “new” names for his philosophy and simply declares that his views and those of Mach are “idealist” (ibid., p. 326)! He traces his genealogy directly to Berkeley and Hume. The philosophy of Pearson, as we shall repeatedly find, is distinguished from that of Mach by its far greater integrity and consistency.
Mach explicitly declares his solidarity with the French physicists, Pierre Duhem and Henri Poincaré . We shall have occasion to deal with the particularly confused and inconsistent philosophical views of these writers in the chapter on the new physics. Here we shall content ourselves with noting that for Poincaré things are “groups of sensations” and that a similar view is casually expressed by Duhem.
We shall now proceed to examine how Mach and Avenarius, having admitted the idealist character of their original views, corrected them in their subsequent works.
 E. Mach, Die Geschichte und die Wurzel des Satzes von der Erhaltung der Arbeit. Vortrag, gehalten in der k. Böhm. Gesellschaft der Wissenschaften am 15. Nov. 1871 [History and Roots of the Principle of the Conservation of Work. A Lecture Delivered at the Bohemian Royal Scientific Society on November 15, 1871], Prag, 1872, S. 57-58.] —Lenin
 E. Mach, Die Mechanik in ihrer Entwicklung historisch-kritisch dargestellt [Mechanics, a Historical and Critical Account of Its Development], 3. Auflage, Leipzig, 1897, S. 473. —Lenin
 Fr. Engels, Herrn Eugen Dührings Umwälzung der Wissenschaft [Herr Eugen Dühring’s Revolution in Science], 3, Auflage, Stuttgart, 1904, S. 6. —Lenin
 Analysis of Sensations —Lenin
 E. Mach, Erkenntnis und Irrtum, 2. Auflage, 1906, S. 12, Anmerkung. 1 —Lenin
 F. Van Cauwelaert, “L’empiriocriticisme” [“Empirio-Criticism”], in Revue néo-scolastique, 1907, Feb., p. 51. —Lenin
 Rudolf Willy, Gegen die Schulweisheit. Eine Kritik der Philosophie [Against School Wisdom. A Critique of Philosophy], München. 1905. S. 170. —Lenin
 A. Bogdanov, The Fundamental Elements of the Historical Outlook on Nature, St. Petersburg, 1899, p. 216. —Lenin
 Karl Pearson, The Grammar of Science, 2nd ed., London, 1900, p. 326. —Lenin
 Analysis of Sensations, p. 4. Cf. Preface to Erkenntnis und Irrtum, 2nd ed. —Lenin
 Henri Poincaré, La valeur de la science (The Value of Science), Paris, 1905 (There is a Russian translation), passim. —Lenin
 P. Duhem, La théorie physique, son objet et sa structure (The Physical Theory, Its Object and Structure), Paris, 1906. Cf. pp. 6 and 10. —Lenin
 See F. Engels, Anti-Dürhring, Moscow, 1959, pp. 34, 53-54.
 Revue néo-scolastique (Neo-scholastic Review)èa heological- philosophical magazine founded by the Catholic philosophical society in Louvain (Belgium), published from 1894 o 1909 under the editorship of Cardinal Mercier. It is now issued under the title of Revue philosophique de Louvain (Philosophical Review of Louvain).