We have seen that Marx in 1845 and Engels in 1888 and 1892 placed the criterion of practice at the basis of the materialist theory of knowledge. “The dispute over the reality or non-reality of thinking which is isolated from practice is a purely scholastic question,” says Marx in his second Thesis on Feuerbach. The best refutation of Kantian and Humean agnosticism as well as of other philosophical crotchets (Schrullen) is practice, repeats Engels. “The result of our action proves the conformity (Uebereinstimmung) of our perceptions with the objective nature of the things perceived,” he says in reply to the agnostics.
Compare this with Mach’s argument about the criterion of practice: “In the common way of thinking and speaking appearance, illusion, is usually contrasted with reality. A pencil held in front of us in the air is seen as straight; when we dip it slantwise into water we see it as crooked. In the latter case we say that the pencil appears crooked but in reality it is straight. But what entitles us to declare one fact to be the reality, and to degrade the other to an appearance?. . . Our expectation is deceived when we fall into the natural error of expecting what we are accustomed to although the case is unusual. The facts are not to blame for that. In these cases, to speak of appearance may have a practical significance, but not a scientific significance. Similarly, the question which is often asked, whether the world is real or whether we merely dream it, is devoid of all scientific significance. Even the wildest dream is a fact as much as any other” (Analysis of Sensations, pp. 18-19).
It is true that not only is the wildest dream a fact, but also the wildest philosophy. No doubt of this is possible after an acquaintance with the philosophy of Ernst Mach. Egregious sophist that he is, he confounds the scientific-historical and psychological investigation of human errors, of every “wild dream” of humanity, such as belief in sprites, hobgoblins, and so forth, with the epistemological distinction between truth and “wildness.” It is as if an economist were to say that both Senior’s theory that the whole profit of the capitalist is obtained from the “last hour” of the worker’s labour and Marx’s theory are both facts, and that from the standpoint of science there is no point in asking which theory expresses objective truth and which—the prejudice of the bourgeoisie and the venality of its professors. The tanner Joseph Dietzgen regarded the scientific, i.e., the materialist, theory of knowledge as a “universal weapon against religious belief” (Kleinere philosophische Schriften [Smaller Philosophical Essays], S. 55), but for the professor-in-ordinary Ernst Mach the distinction between the materialist and the subjective-idealist theories of knowledge “is devoid of all scientific significance”! That science is non partisan in the struggle of materialism against idealism and religion is a favourite idea not only of Mach but of all modern bourgeois professors, who are, as Dietzgen justly expresses it, “graduated flunkeys who stupefy the people by their twisted idealism” (op. cit., p. 53
And a twisted professorial idealism it is, indeed, when the criterion of practice, which for every one of us distinguishes illusion from reality, is removed by Mach from the realm of science, from the realm of the theory of knowledge. Human practice proves the correctness of the materialist theory of knowledge, said Marx and Engels, who dubbed all attempts to solve the fundamental question of epistemology without the aid of practice “scholastic” and “philosophical crotchets.” But for Mach practice is one thing and the theory of knowledge another. They can be placed side by side without making the latter conditional on the former. In his last work, Knowledge and Error, Mach says: “Knowledge is a biologically useful (förderndes) mental experience” (2nd Germ. ed., p. 115). “Only success can separate knowledge from error” (p. 116). “The concept is a physical working hypothesis” (p. 143). In their astonishing naïveté our Russian Machian would-be Marxists regard such phrases of Mach’s as proof that he comes close to Marxism. But Mach here comes just as close to Marxism as Bismarck to the labour movement, or Bishop Eulogius to democracy. With Mach such propositions stand side by side with his idealist theory of knowledge and do not determine the choice of one or another definite line of epistemology. Knowledge can be useful biologically, useful in human practice, useful for the preservation of life, for the preservation of the species, only when it reflects objective truth, truth which is independent of man. For the materialist the “success” of human practice proves the correspondence between our ideas and the objective nature of the things we perceive. For the solipsist “success” is everything needed by me in practice, which can be regarded separately from the theory of knowledge. If we include the criterion of practice in the foundation of the theory of knowledge we inevitably arrive at materialism, says the Marxist. Let practice be materialist, says Mach, but theory is another matter.
"In practice," Mach writes in the Analysis of Sensations, "we can as little do without the idea of the self when we perform any act, as we can do without the idea of a body when we grasp at a thing. Physiologically we remain egoists and materialists with the same constancy as we forever see the sun rising again. But theoretically this view cannot be adhered to" (284-85).
Egoism is beside the point here, for egoism is not an epistemological cateogry. The question of the appartent movement of the sun around the earth is also beside the point, for in practice, which serves us as a criterion in the theory of knowledge, we must include also the practice of astronomical observations, discovereies, etc. There remains only Mach’s valuable admission that in their practical life men are entirely and exclusively guided by the materialist theory of knowledge; the attempt to obviate it "theoretically" is characteristic of Mach’s gelehrte scholastic and twisted idealistic endeavours.
How little of a novelty are these efforts to eliminate practice–as something unsusceptible to epistemological treatment–in order to make room for agnosticism and idealism is show by the following example from the history of German classical philosophy. Between Kan and Fichte stands G. E. Schulze (known in the history of philosophy as Schulze-Aenesidemus). He openly advocates the skeptical trend in philosophy and calls himself a follower of Hume) and of the ancients Pyrrho and Sextus). He emphatically rejects every thing-in-itself and the possibility of objective knowledge, and emphatically insists that we should not go beyond “experience,” beyond sensations, in which connection he anticipates the following objection from the other camp: “Since the sceptic when he takes part in the affairs of life assumes as indubitable the reality of objective things, behaves accordingly, and thus admits a criterion of truth, his own behaviour is the best and clearest refutation of his scepticism.”—[G. E. Schulze, Aenesidemus oder über die Fundemente der von dem Herrn Professor Reinhold in Jena gelieferten Elementarphilosophie [Aenesidemus, or the Fundamentals of the Elementary Philosophy Propounded by Professor Reinhold in Jena], 1792, S. 253.] “Such proofs,” Schulze indignantly retorts, “are only valid for the mob (Pöbel).” For “my scepticism does not concern the requirements of practical life, but remains within the bounds of philosophy” (pp. 254, 255).
In similar manner, the subjective idealist Fichte also hopes to find room within the bounds of idealistic philosophy for that “realism which is inevitable (sich aufdringt) for all of us, and even for the most determined idealist, when it comes to action, i.e., the assumption that objects exist quite independently of us and outside us” (Werke, I, 455).
Mach’s recent positivism has not traveled far from Schulze and Fichte! Let us note as a curiosity that on this question too for Bazarov there is no one but Plekhanov—there is no beast stronger than the cat. Bazarov ridicules the “salto vitale philosophy of Plekhanov” (Studies, etc., p. 69), who indeed made the absurd remark that “belief” in the existence of the outer world “is an inevitable salto vitale” (vital leap) of philosophy (Notes on Ludwig Feuerbach, p. III). The word “belief” (taken from Hume), although put in quotation marks, discloses a confusion of terms on Plekhanov’s part. There can be no question about that. But what has Plekhanov got to do with it? Why did not Bazarov take some other materialist, Feuerbach, for instance? Is it only because he does not know him? But ignorance is no argument. Feuerbach also, like Marx and Engels, makes an impermissible—from the point of view of Schulze, Fichte and Mach—“leap” to practice in the fundamental problems of epistemology. Criticising idealism, Feuerbach explains its essential nature by the following striking quotation from Fichte, which superbly demolishes Machism: “‘Youassume,’ writes Fichte, ‘that things are real, that they exist outside of you, only because you see them, hear them and touch them. But vision, touch and hearing are only sensations. . . . You perceive, not the objects, but only your sensations’” (Feuerbach, Werke, X. Band, S. 185). To which Feuerbach replies that a human being is not an abstract ego, but either a man or woman, and the question whether the world is sensation can be compared to the question: is the man or woman my sensation, or do our relations in practical life prove the contrary? “This is the, fundamental defect of idealism: it asks and answers the question of objectivity and subjectivity, of the reality or unreality of the world, only from the standpoint of theory” (ibid., p. 189). Feuerbach makes the sum-total of human practice the basis of the theory of knowledge. He says that idealists of course also recognise the reality of the I and the Thou in practical life. For the idealists “this point of view is valid only for practical life and not for speculation. But a speculation which contradicts life, which makes the standpoint of death, of a soul separated from the body, the standpoint of truth, is a dead and false speculation” (p. 192). Before we perceive, we breathe; we cannot exist without air, food and drink.
“Does this mean that we must deal with questions of food and drink when examining the problem of the ideality or reality of the world?—exclaims the indignant idealist. How vile! What an offence against good manners soundly to berate materialism in the scientific sense from the chair of philosophy and the pulpit of theology, only to practise materialism with all one’s heart and soul in the crudest form at the table d’h(tm)te” (p. 195). And Feuerbach exclaims that to identify subjective sensation with the objective world “is to identify pollution with procreation” (p. 198).
A comment not of the politest order, but it hits the vital spot of those philosophers who teach that sense-perception is the reality existing outside us.
The standpoint of life, of practice, should be first and fundamental in the theory of knowledge. And it inevitably leads to materialism, brushing aside the endless fabrications of professorial scholasticism. Of course, we must not forget that the criterion of practice can never, in the nature of things, either confirm or refute any human idea completely. This criterion also is sufficiently “indefinite” not to allow human knowledge to become “absolute,” but at the same time it is sufficiently definite to wage a ruthless fight on all varieties of idealism and agnosticism. If what our practice confirms is the sole, ultimate and objective truth, then from this must follow the recognition that the only path to this truth is the path of science, which holds the materialist point of view. For instance, Bogdanov is prepared to recognise Marx’s theory of the circulation of money as an objective truth only for “our time,” and calls it “dogmatism” to at tribute to this theory a “super-historically objective” truth (Empirio-Monism, Bk. III, p. vii). This is again a muddle. The correspondence of this theory to practice cannot be altered by any future circumstances, for the same simple reason that makes it an eternal truth that Napoleon died on May 5, 1821. But inasmuch as the criterion of practice, i.e., the course of development of all capitalist countries in the last few decades, proves only the objective truth of Marx’s whole social and economic theory in general, and not merely of one or other of its parts, formulations, etc., it is clear that to talk of the “dogmatism” of the Marxists is to make an unpardonable concession to bourgeois economics. The sole conclusion to be drawn from the opinion of the Marxists that Marx’s theory is an objective truth is that by following the path of Marxist theory we shall draw closer and closer to objective truth (without ever exhausting it); but by following any other path we shall arrive at nothing but confusion and lies.
 Lenin is referring to Marx’s “Theses on Feuerbach” (1845) and to the works by F. Engels: Ludwig Feuerbach end the End of Classical German Philosophy (1388) and the “Special Introduction to the English Edition of 1892” of his Socielism: Utopian and Scientific (see K. Marx and F. Bagels, Selected Works, Vol. II, Moscow, 1958, pp. 403-05, 358-403, 93-115).
 See K. Marx and F. Engels, Selected Works, Vol. II, Moscow, 1958, pp. 403, 101.
 Bishop Eulogius member of the State Duma, a monarchist and extreme reactionary.