Joseph Dietzgen 1878

Our Professors on the Limits of Cognition

First published: in Vorwarts, 1878;
Source: “Joseph Dietzgen, Philosophical Essays” (ed. Eugen Dietzgen & Joseph Dietzgen Jr.), Charles H. Kerr & Co., Chicago 1906, pp. 236-253.
Translated: by Theodore Rothstein & Max Beer.
Transcribed: by Einde O’Callaghan for the Marxists Internet Archive.


At the “Fiftieth Meeting of German Naturalists and Physicians,” held at Munich, September, 1877, Professor C.V. Nägeli, of Munich, took up a well known lecture of his Berlin colleague, Du Bois-Reymond, and delivered a remarkable address on the Limits of Scientific Knowledge. One is bound to admit that the Munich professor has, in point of truth and clearness, far surpassed his Berlin colleague; still he, too, was unable to rise to the level of his time.

He nearly explained the whole thing; but the small point which he missed at the conclusion is just the vital point, – the one which marks the wide gulf that divides physics from metaphysics, sober science from romantic belief. Such a lecture, proceeding as it does sharply up to that point, offers a welcome opportunity to show once more the superiority of the Social-Democratic conception of the world.

Prof. Nägeli treats his subject in the following manner:

“Many methodical scientists who, by their exact mode of research, augment the stock of well based facts, while holding a fundamental solution inadmissible, answer the question as to the Limits of Knowledge of Nature by a simple statement of fact: ‘Belief invariably begins where knowledge ends.’ The statement that our belief begins where knowledge ends – the lecturer continues – is a practical solution for certain definite purposes. Our interest is not satisfied thereby. We turn our special attention to the theoretical side of the problem. We want to know whether the limits where human knowledge must stop are at all definable, and if so, how far can knowledge penetrate into the domain of Nature; how much of Nature could the human mind conceive, if it were to occupy itself during an unlimited time – say, an eternity – with natural sciences and have at its command all imaginable means of research, – in a word, what is the fundamental line of demarkation between the domain of knowledge and that of belief?”

As is well known, his predecessor, Du Bois-Reymond, tried to prove that there really is such an impassable line of demarkation, that consequently belief will, under all circumstances, have a domain of its own left to it. It is only owing to the reservation of this little refuge for religious romanticism that his lecture has gained its seeming importance and popularity. Since that time the champions of the Inconceivable have not ceased singing Hosanna. True enough, Prof. Nägeli is little edified by this song, but his official privileged position as a professor does not allow him to enter the fight in a whole hearted manner. After showing his predecessor clearly and by all manner of means that he has misunderstood the nature of scientific knowledge, he concludes as follows: “Du Bois-Reymond winds up his lecture with the crushing words, Ignoramus and Ignorabimus. I should like to conclude mine with the qualified, but withal, consoling expression of opinion that the fruit of our researches is not merely knowledge, but actual truth which contains within itself the germ of an almost (!) infinite growth, without thereby coming nearer by the smallest step to omniscience. If we adopt an attitude of a reasonable resignation, if we, as finite and transient beings that we are, content ourselves with human knowledge instead of claiming divine cognition, then we may say with full confidence in ourselves and in the future: ‘We know and we shall know.’”

These concluding remarks contain the essence of the question. They also unmistakably express both the religious and subservient consciousness of the Berlin professor and the tame and timid inconsistency of the Munich one. The religious romanticism of Du Bois-Reymond calls all results of scientific research “merely knowledge,” and not “real truth.” Such true cognition is not attainable by the poor human understanding. The professor literally says that “the whole of our knowledge of Nature is in reality not cognition, but a substitute of an interpretation.”

Our science, then, can only yield chicory instead of coffee. Our scientific interpretation may very well allow itself to be buried, perhaps it may rise transfigured on the day of judgment. And such reactionary word-splitting wants to dominate our universities!

Then comes the other one, Nägeli, to whom that pious resignation seems rather too strong. The nice distinction between knowledge and cognition does not recommend itself to him. He is convinced that “we know and shall know.” But observe how gently he breaks this news to us: “without thereby coming nearer to omniscience by the smallest step.” He, too speaks humbly of “human” cognition as against that of the higher Non-Humanity. We must submit to a “rational” resignation and lay no claim to “divine knowledge.” Is it possible that so learned a professor should “resign” himself monklike to divine cognition and even call such resignation rational? All natural cognition is divine, that is, glorious and wonderful. When, however, our professor opposes to human cognition a divine one, then he proceeds beyond the limits of Nature and lands in the same romanticism in which his predecessor has landed before him.


The Munich professor has clearly shown to his Berlin colleague that by not recognizing our knowledge of Nature as a real, true cognition, he demonstrated not the limits, but the inanity or absolute impossibility of scien tific cognition. And, consequently, he stands at a purely negative point of view. According to Nägeli, Du Bois-Reymond teaches as follows:

Cognition of Nature is the reduction of a natural phenomenon to the mechanics of simple, indivisible atoms.

Atoms in this sense do not exist and, consequently, no real cognition exists.

Even if the world could be understood out of the mechanics of the atoms we would still be unable to understand out of these atoms apperception and consciousness.

On this Nägeli justly remarks: “Since the speaker does not proceed beyond mere negation, natural science cannot, in its lack of a proper domain, draw its limits either, – and if it is for ever unable to gain an insight even in the material phenomena, it matters little whether it may possibly lay claim to the spiritual domain.” In other words, if our knowledge yields instead of coffee only chicory, then we only have one bad brew and nothing else. There is nothing good left which it would be worth while to investigate, to understand or to place within its proper limits.

After one professor has thus settled the other, the pleasant duty remains for us to show, what, however, must be clear already, that the Munich professor, too, has landed where the other one was caught. Herr Nägeli differs from Du Bois-Reymond in that he has so far broken loose that it is difficult to judge whether it was because his strength has failed him or on account of decorum, that he felt himself obliged to keep to the “mysterious land of presentiment,” to the “divine cognition and omniscience” and such like things which “surpass our human faculties.”

“As regards the faculty of the Ego to know of natural things, the decisive and undoubted fact is that, however our faculty of thinking is constituted, only the sensory perception offers us any knowledge of Nature. If we did not see and hear, did not taste, smell or touch anything we could not altogether know that something exists outside us, – nay, that we ourselves are corporeal.”

These are brave words. Let us adhere to them and see whether our professor sticks to them also.

Our sensory perception, says our lecturer, is limited to the present.

“We cannot in a direct way perceive what was in the past and what will be in the future, nor what is too distant in space nor what is too small or too large in dimension.”

Quite so. But what one man did not see yesterday another one will see to-morrow. Where the distances are too great and the dimensions too small, there we call to our assistance the telescope and the miscroscope. “Thus it is possible, theoretically speaking, for the human organism to get bodily impressions of all phe nomena in Nature. But how does it stand in reality? What impressions are powerful enough to be noticeable to us and what are insignificant enough to pass by unnoticed?”

We are not going to follow the lecturer in all his deails, but will readily acknowledge what always has to be acknowledged,

“Our faculty to get direct perception of Nature through the senses is limited in two respects. We probably (!) lack the perception for whole domains of Nature (is it for that of goblins, ghosts and the like? – J.D.) and so far as we possess it, it merely embraces in time and space an insignificant portion of the whole.” (Yes, Nature surpasses the human mind, it is an inexhaustible object, – J.D.) “Of the constitution, properties, history of a fixed star of the last magnitude, of the organic life on its obscure satellites, of the material and spiritual movements in those organisms – of all that we shall never know anything.”

Here, again, our professor goes too far. Our faculty of research is only limited in so far as its object, Nature, is unlimited. We cannot arrive at any end, simply be cause there is no end. But where there is an end, there we may possibly arrive. No professor can tell how much of the fixed stars and their satellites we and our successors may yet find out, how infinitely deep we may yet penetrate into the past, into the future and into the small est particles, since, as Nägeli himself says, we have “theoretically” speaking, every possibility for that. We know that no explorer will ever find two mountains with out a valley, no cutter will ever make a knife without a blade and handle, for these are all theoretical impossibilities. But what results practice will still achieve – to determine that in advance, after the spectral analysis and the invention of the telephone, is surely a piece of impertinence.


Inquiry never arrives at an end – neither objectively nor subjectively; neither the infinity of the world, nor the infinity of the intellect admit of an end; that, however, the intellect is but a limited portion of the world, no Social-Democratic materialist will ever deny. On the contrary, it is precisely he who scientifically conceived the thinking faculty as an instrument, quality, product or part of Nature. We are not animated to such a presumptuous extent by mind as to ascribe to it every capacity and every faculty. We only wish – what our professor wished, but could not achieve – we only wish to escape from dualism. We can only acknowledge one solitary world – the one “of which we obtain knowledge through the sensory perception.” We keep Nägeli to his word, namely, where we do not see or hear or feel or taste or smell anything, there we can not know anything either.

I wish to return once more in a positive manner to the perceptibly limited nature of human cognition. With this faculty we can only know; to sing, to jump and to do a hundred other things with it we cannot; in so far reason is limited. But in its own element, in cognition, it is unlimited, and so unlimited that it never comes to an end with its work.

To go on. Everything knowable is open to it. The unknowable, that which is absolutely inaccessible to the senses, is for us non-existent; it is also “in itself “ non-existent insofar as we cannot even speak of it without drawing upon the fanciful.

“Our senses are just organized for the needs of common life, but not in order to satisfy our mental need, and to give us knowledge of all phenomena of Nature. ... Just as we came to know something about the phenomena which have their seat in every particle of matter, so there may be yet other natural forces, other molecular forces of motion of which we do not get any sensory impression, because they never unite into an observable sum, and therefore remain hidden from us.”

We reply: Those who have the ‘mental need’ to know something of phenomena ‘which remain hidden from us,’ and must remain hidden according to our Nature, have not a mental need, but a mystical need. The electrical phenomena have no more been discovered by accident than America was. And what a strange Columbus a scientist must be to speak of phenomena which nobody ever perceived or will perceive. It is possible that Mephistopheles should hover about me in the form of an invisible rearmouse; but what I don’t know leaves me cool and ought also to leave cool every natural philosopher.

Nägeli says:

“The natural philosopher must well be aware that his inquiry is confined in all respects by finite limits, that on all sides he is categorically bidden to halt by the unknowable eternity. That this has not always been understood, that the infinitely great and the infinitely small have been mistaken for the endless and nothing, has often led to erroneous ideas. Such are the erroneous theories of the physical atoms as the infinitely small, and of the beginning and end of the world as the infinitely great.”

The consciousness of the limits of research may, eventually, be useful to the scientific inquirer. Still our professor ought not to have forgotten that rational doctrine in the very same breath in which he propounded it. This he does when saying that “on all sides we are categorically ordered to halt by the unknowable eternity.” How can one know anything about this halt when it is unknowable? Or is Nägeli, like Du Bois, perhaps, unable to escape from the mere negation? Can he, too, only tell of the great halting-point of the ‘eternal’ that nothing can be known about it?

Nägeli continues.

“This is not to say that the scientist must not philosophise, that he must not enter the domain of the ideal and transcendental. But he ceases to be a scientist, and the use he can make of his own profession is to keep the two domains strictly apart, that he treats the one as the real domain of research and knowledge, and the other, freed as it is of all finite, as the occult domain of presentiment.”

Our good professor knows the philosophers badly if he thinks that they will content themselves with the ‘occult domain of presentiment.’ Not only the Social-Democrat, but also many ‘official’ philosophers, claim that although their domain be hidden from the Munich professor, it is still open to ‘human understanding,’ and that all ‘divine cognition’ must be rigorously excluded from it. The occult domain or the metaphysical world beyond is not nearer Philosophy than to the other pure ideologists who seek each and every one to find some snug corner for their shrines. With science these conservative endeavors have nothing to do; they belong to the domain of practice. On the other hand, there is much more that belongs to the domain of exact science than those gentlemen are at all inclined to admit. They consider the conception of Nature in too vague a fashion. If it cannot be disputed that History, Economics, Politics, etc., ought to develop into exact sciences, nay, are already in a fair way to do so and have already partially done so, then Social-Democracy can also prove that the gulf between Philosophy and Science has already been bridged over without the bourgeois geniuses getting the slightest wind of it.

Professor Steinthal has gone in this respect further than his scientific colleagues. In the third edition of his book, The Origin of Speech, he says: “Speaking is not thinking, but the means, the organ of thinking,” and “no mind is without speech (designation); speech itself already belongs to the domain of mind.” Continuing this train of thought we argue: Speech lends our ideas their true designation. What speech designates as Nature, truth, knowledge and tin is really and truly tin, knowledge, truth and Nature. Steinthal teaches us on this point as follows: A only equals A and never B, if ‘equal’ is not taken in the mathematical sense of being equal in magnitude. But if equal means equality in essence, then A equalling B, B must be A, and we have no right to call it otherwise than A. Steinthal calls this “the principle of research and knowledge.” In other words unity, unity in conception and name is the first condition of science. All dualism is untenable. If divine knowledge = A, and human knowledge = B, that is, if both are essentially different, then we simply juggle with the word knowledge in a dualistic manner. Just as all mankind, in spite of the different races, make but one species, so necessarily is there in spite of the diverse kinds but one knowledge, one truth, one Nature, – the true Nature, the natural truth. And everything we get to know in heavens, on earth and in other places belongs to the same category. And what we do not get to know and of which only the parson and the professor tell us, – is mere jugglery, which, however, belongs to the natural truth, that is, true jugglery.


Nothing more is meant by these deductions than this: the world is a unity, that is, there is only one world. And whoever wants to pass over to another world – from that of experience to that of presentiment or divinity, – nay, whoever merely speaks of it, is either a ‘crank’ or a scamp or a deceiver of the people. To have the right to stigmatise an opponent with one of these bad names no further proof is required than that he contradicts the “wants of Reason for unity.”

When Nägeli tries to impose upon his colleagues at the meeting of scientists the belief that our intellect has, or, perhaps, has outside of the bounds of its own nature yet other, supernatural or unnatural limits, he performs thereby a scandalous trick, the more scandalous, in fact, the further he has progressed in the conception that Nature represents an organic whole where no gulf could be found.

“Our knowledge of Nature is thus always a mathematical one and is based either on simple measurement, such as in morphological and descriptive sciences, or on a measurement of causation as in physical and physiological sciences. But with the assistance of mathematics, of measure, weight and number only relative or quantitative differences can be understood ... Real qualitative differences we cannot determine since qualities can not be compared. This is an important fact for the knowledge of Nature. It follows from this fact that if there are in Nature qualitatively or absolutely different domains, scientific knowledge is only possible in an isolated way within the bounds of each of them, and no connecting bridge leads from one domain into another. But from the same fact also follows that in so far as we can investigate Nature connectedly, in so far as our measuring knowledge proceeds in a consistent, uninterrupted way, and as we come to an understanding of one phenomenon by means of another ... absolute differences, impassable gulfs do not exist in Nature at all.”

This passage shows how very near our Munich professor came to a right and complete conception of the nature of knowledge. It is only wanted to dot the i’s and to cross the t’s. This little thing however, is of infinite importance, since without it one always slides back into the intolerable error of wishing to formulate absolute or qualitative differences, to separate by an impassible gulf the finite and infinite or the human and divine knowledge, and to describe two domains without a connecting bridge.

This dualistic scandal must once for all be put an end to by going one little step further than Nägeli. The faculty of cognition must be recognised as the faculty which embraces all differences, all qualities as a unity, as one solitary quantity. It is rational means: reason makes of all existence one order. To enroll under this order all the phenomena of the world as different species, is to know Nature. Because the intellect can do this, because it divides everything into orders and species, into subjects and predicates so that finally only one order remains, only one subject, Being or the Given Premises of which mind and body, reason, fancy, matter, force, etc., are predicates or species, – because of that there cannot possibly remain in the world any impassable gulf. Everything must reduce itself to a theoretical harmony, to one system.

As soon as this i is dotted, it becomes no longer possible to talk grandiloquently that there can be an absolute difference or impassable gulf between the inorganic and organic, between plant, animal, ape, man, mental and manual work, etc. One must know that two drops of water are just as infinitely different as animal and man, as body and soul, and that separation and differentiation are just as little limited as “striving after unity.”

I should like to make the reader understand what the professors, so far as I know them, have not yet understood, viz., that our intellect is a dialectical instrument, an instrument which reconciles all opposites. The intellect creates unity by means of the variety and comprehends the difference in the equality. Hegel has made it clear long ago that in science there is no either – or, but as well as. The faculty of knowledge in the ape, the rustic and the scientist is just of the same category as that in the philosopher, and also the most divine knowledge belongs to the same category, and are all forms of one variety, varieties of one order, predicates of one subject. It is certainly admissible to distinguish between the human and the animal intellect, to raise the former to the skies and give it a different name. But it is just as inadmissible to create an impassable gulf between reason and instinct. If we reason soberly and do not indulge in extravagant exclamations we are bound to recognise that the faculty of discrimination separates infinitely but also connects endlessly.

Nägeli says:

“It is a logical necessity for the scientist to allow in the finite Nature only gradual distinctions.” Our reply to this is: it is a logical necessity to throw the infinite and the finite into the same heap, that is to conceive of Nature as a unity which is both finite and infinite.

“But what is the world which is dominated by the human mind? Not even a grain of sand in the eternity of space, not even a second in the eternity of time, but is an outwork of the true essence of the All.” That’s exactly the language of the parson. And it is quite true, if it is only meant as an emphatic expression of sentiment in view of the greatness of existence; but is also very insipid, if the professor takes it to mean that our space and our time were not part and parcel of the infinite and eternal, – very insipid, if it is meant to express that the ‘true essence of the All’ is hidden beyond the phenomena in the infathomable region of metaphysics or religion. The All is to be found in its moments, and to seek it elsewhere is a task which Social-Democrats willingly leave to the ruling classes.


After Prof. Nägeli had thus tried to curb our scientific knowledge of Nature his example was followed at the same meeting by Prof. Virchow in order to restrict still further the “freedom of science in the modern State.” His eyes are so sensitive that they cannot stand even the feeble light which Nägeli had put up.

“I should like to prove to you that we have arrived at a point where we must make it our special business to moderate ourselves and to renounce to a certain extent our predilections and personal views so as to keep up the good temper which the nation still exhibits towards us.”

What a miserable “nation” this is, whose good temper the professor desires to preserve, will prove no puzzle to our comrades. We recognise the well-to-do by this mere predilection for the moderation of others, by their sensitiveness to everything which may interfere with their digestion.

“It goes without saying that we must demand for everything which we consider to be well established scientific truth complete adoption in the national store of knowledge; this the nation must absorb, – this it must consume and digest.”

Our professor is right; there are some truths which are too patent to allow of being hushed up, and there are others which can serve the revolutionary tendencies and must, therefore be “moderated,” though science unmistakably gravitates to them.

“We cannot proceed to explain to every yokel: this is true, established by fact, this is fairly known and that is only a conjecture ... We must abstain from putting into the heads of our schoolmasters what w merely conjecture ... After all, this theory ol evolution, too, when consistently carried to its logical conclusion, has some very dangerous aspects, and it will not have escaped your attention, I hope, that Social-Democracy has taken cognizance of it.”

This hardly requires any comment. One needs only listen to the man to perceive at once how it stands with the “Freedom of science in the modern State.” Knowledge must naturally be still more restricted by Virchow than it was by his colleague, Nägeli.

“In thus narrowing the limits of our knowledge we must remember above all that what is commonly called natural science is like all other knowledge in the world made up of three heterogeneous elements. Usually we merely distinguish between objective and subjective knowledge. Yet we have still a third, a sort of medium element, namely, that of belief, which, as you know, also exists in science.”

This subtle distinction which the artful dodger, for the sake of his reputation, thereupon draws between scientific and religious belief, need not be taken seriously, but the ingenious way in which he scents the weak points of his predecessor deserves some acknowledgement. Nägeli had said:

“Reflex action is clearly bound up in higher animals with sensitiveness. We must also grant it in the case of lower animals, and we have no reason to deny it in case of plants and inorganic bodies ... In virtue of its structure out of different parts the atom possesses various properties and powers, accordingly it also exercises various influences (attraction and repulsion) upon other atoms ... If, therefore, the molecules experience something akin to sensitiveness it must also be a pleasure to them if they can follow their sympathies and antipathies, etc. ... The molecules of chemical elements are, therefore, swayed by a number of qualitatively and quantitatively different sensations. We accordingly find in the lowest and simplest organizations of matter of which we know, essentially the same phenomena as in the highest ... The difference is merely that of degree.”

To that Virchow replied:

“This is the objection which I make to the statements of Herr Nägeli ... He not only wants us to extend the domain of mind to animals and plants, but also that we finally pass with our views of the nature of mental phenomena from the organic to the inorganic world ... If mental phenomena are at all costs to be brought in connection with those of the rest of the world, then one necessarily arrives at transferring first the psychical phenomena as they are found in man and the highest organized vertebra to the lower and ever lower animals, and then to endow even plants with a soul; then it is the cell which feels and thinks, and finally there is a gradual transition even to the chemical atoms which hate and love each other, seek or avoid each other ... I do not object to atoms of carbon also having a mind, ... but I do not see anything by which it could be known. It is a mere play upon words. By declaring attraction and repulsion to be mental, psychical phenomena we simply throw the psychical overboard ... To us the sum total of psychical phenomena is undoubtedly only associated with certain animals and not with the whole of organic life, not even with all animals. This I declare without hesitation.”

We must acknowledge that Virchow is in one respect perfectly right: ideas with a distinct meaning in language should remain distinct. One must not play with words; but neither must one shut his eyes to the fact that the psychical sensation of pleasure and pain presents a certain analogy to the chemical attraction and repulsion. Let us only dot the i, and then the two will appear as equally legitimate forms of the same Nature, as the equally intelligible predicate of the same subject. Only those who utterly refuse to connect the mental phenomena with those of the rest of the world, will fail to perceive that the animal and chemical, the physical and psychical phenomena are common varieties of the great world process. And once more, gentlemen: The world is dialectical, as much one or homogeneous in essence as varied in the manner it appears; all distinction is only that of degree. The unity which Nägeli defends is lost to him as soon as he lands in “the world of presentiment” and at “divine omniscience;” but that unity is already lost to Virchow when he merely arrives at the distinction between organic and inorganic; still more intolerable is to him the link between animal and man; and as for the opposition between body and soul, – this he wants to keep outside the province of debate altogether, as the bridging over of this opposition “in the head of the Socialist” was bound to cause an awful confusion and lead to the overthrow of all professorial wisdom.