The first of these questions is constantly being hurled by the idealists and agnostics, including the Machians, at the materialists; the second question by the materialists at the Machians. Let us try to make the point at issue clear.
Avenarius says on the subject of matter:
“Within the purified, ‘complete experience’ there is nothing ‘physical’—‘matter’ in the metaphysical absolute conception—for ‘matter’ according to this conception is only an abstraction; it would be the total of the counter-terms abstracted from every central term. Just as in the principal co-ordination, that is, ‘complete experience,’ a counter-term is inconceivable (undenkbar) without a central term, so ‘matter’ in the metaphysical absolute conception is a complete chimera (Unding)” (Bemerkungen [Notes], S. 2, in the journal cited, § 119).
In all this gibberish one thing is evident, namely, that Avenarius designates the physical or matter by the terms absolute and metaphysics, for, according to his theory of the principal co-ordination (or, in the new way, “complete expcrience"), the counter-term is inseparable from the central term, the environment from the self; the non-self is inseparable from the self (as J. G. Fichte said). That this theory is disguised subjective idealism we have already shown, and the nature of Avenarius’ attacks on “matter” is quite obvious: the idealist denies physical being that is independent of the mind and therefore rejects the concept elaborated by philosophy for such being. That matter is “physical” (i.e.., that which is most familiar and immediately given to man, and the existence of which no one save an inmate of a lunatic asylum can doubt) is not denied by Avenarius; he only insists on the acceptance of “his” theory of the indissoluble connection between the environment and the self.
Mach expresses the same thought more simply, without philosophical flourishes: “What we call matter is a certain systematic combination of the elements (sensations)” (Analysis of Sensations, p. 265). Mach thinks that by this assertion he is effecting a “radical change” in the usual world outlook. In reality this is the old, old subjective idealism, the nakedness of which is concealed by the word “element.”
And lastly, the English Machian, Pearson, a rabid antagonist of materialism, says: “Now there can be no scientific objection to our classifying certain more or less permanent groups of sense-impressions together and terming them matter,—to do so indeed leads us very near to John Stuart Mill’s definition of matter as a ‘permanent possibility of sensation,’—but this definition of matter then leads us entirely away from matter as the thing which moves” (The Grammar of Science, 2nd ed., 1900, p. 249). Here there is not even the fig-leaf of the “elements,” and the idealist openly stretches out a hand to the agnostic.
As the reader sees, all these arguments of the founders of empirio-criticism entirely and exclusively revolve around the old epistemological question of the relation of thinking to being, of sensation to the physical. It required the extreme naïveté of the Russian Machians to discern anything here that is even remotely related to “recent science,” or “recent positivism.” All the philosophers mentioned by us, some frankly, others guardedly, replace the fundamental philosophical line of materialism (from being to thinking, from matter to sensation) by the reverse line of idealism. Their denial of matter is the old answer to epistemological problems, which consists in denying the existence of an external, objective source of our sensations, of an objective reality corresponding to our sensations. On the other hand, the recognition of the philosophical line denied by the idealists and agnostics is expressed in the definitions: matter is that which, acting upon our sense-organs, produces sensation; matter is the objective reality given to us in sensation, and so forth.
Bogdanov, pretending to argue only against Beltov and cravenly ignoring Engels, is indignant at such definitions, which, don’t you see, “prove to be simple repetitions” (Empirio-Monism, Bk. III, p. xvi) of the “formula” (of Engels, our “Marxist” forgets to add) that for one trend in philosophy matter is primary and spirit secondary, while for the other trend the reverse is the case. All the Russian Machians exultantly echo Bogdanov’s “refutation"! But the slightest reflection could have shown these people that it is impossible, in the very nature of the case, to give any definition of these two ultimate concepts of epistemology save one that indicates which of them is taken as primary. What is meant by giving a “definition"? It means essentially to bring a given concept within a more comprehensive concept. For example, when I give the definition “an ass is an animal,” I am bringing the concept “ass” within a more comprehensive concept. The question then is, are there more comprehensive concepts, with which the theory of knowledge could operate, than those of being and thinking, matter and sensation, physical and mental? No. These are the ultimate concepts, the most comprehensive concepts which epistemology has in point of fact so far not surpassed (apart from changes in nomenclature, which are always possible). One must be a charlatan or an utter blockhead to demand a “definition” of these two “series” of concepts of ultimate comprehensiveness which would not be a “mere repetition": one or the other must be taken as the primary. Take the three afore-mentioned arguments on matter. What do they all amount to? To this, that these philosophers proceed from the mental or the self, to the physical, or environment, as from the central term to the counter-term—or from sensation to matter, or from sense-perception to matter. Could Avenarius, Mach and Pearson in fact have given any other “definition” of these fundamental concepts, save by pointing to the trend of their philosophical line? Could they have defined in any other way, in any specific way, what the self is, what sensation is, what sense-perception is? One has only to formulate the question clearly to realise what utter non-sense the Machians are talking when they demand that the materialists give a definition of matter which would not amount to a repetition of the proposition that matter, nature, being, the physical—is primary, and spirit, consciousness, sensation, the psychical—is secondary.
One expression of the genius of Marx and Engels was that they despised pedantic playing with new words, erudite terms, and subtle “isms,” and said simply and plainly: there is a materialist line and an idealist line in philosophy, and between them there are various shades of agnosticism. The painful quest for a “new” point of view in philosophy betrays the same poverty of mind that is revealed in the painful effort to create a “new” theory of value, or a “new” theory of rent, and so forth.
Of Avenarius, his disciple Carstanjen says that he once expressed himself in private conversation as follows: “I know neither the physical nor the mental, but only some third.” To the remark of one writer that the concept of this third was not given by Avenarius, Petzoldt replied: “We know why he could not advance such a concept. The third lacks a counter-concept (Gegenbegriff). . . . The question, what is the third? is illogically put” (Einf. i.d. Ph. d. r. E., II, 329).[Einführung in die Philosophie der reinen Erfahrung [Introduction to the Philosophy of Pure Experience], Vol. II, p. 329. –Ed] Petzoldt understands that an ultimate concept cannot be defined. But he does not understand that the resort to a “third” is a mere subterfuge, for every one of us knows what is physical and what is mental, but none of us knows at present what that “third” is. Avenarius was merely covering up his tracks by this subterfuge and actually was declaring that the self is the primary (central term) and nature (environment) the secondary (counter-term).
Of course, even the antithesis of matter and mind has absolute significance only within the bounds of a very limited field—in this case exclusively within the bounds of the fundamental epistemological problem of what is to be regarded as primary and what as secondary. Beyond these bounds the relative character of this antithesis is indubitable.
Let us now examine how the word “experience” is used in empirio-critical philosophy. The first paragraph of The Critique of Pure Experience expounds the following “assumption": “Any part of our environment stands in relation to human individuals in such a way that, the former having been given, the latter speak of their experience as follows: ‘this is experienced,’ ‘this is an experience’; or ‘it followed from experience,’ or ‘it depends upon experience.’” (Russ. trans., p. 1.) Thus experience is defined in terms of these same concepts: self and environment; while the “doctrine” of their “indissoluble” connection is for the time being tucked out of the way. Further: “The synthetic concept of pure experience"—namely, experience “as a predication for which, in all its components, only parts of the environment serve as a premise” (pp. 1 and 2). If we assume that the environment exists independently of “declarations” and “predications” of man, then it becomes possible to interpret experience in a materialist way! “The analytical concept of pure experience"—"namely, as a predication to which noth ing is admixed that would not be in its turn experience and which, therefore, in itself is nothing but experience” (p. 2). Experience is experience. And there are people who take this quasi-erudite rigmarole for true wisdom!
It is essential to add that in the second volume of The Critique of Pure Experience Avenarius regards “experience” as a “special case” of the mental; that he divides experience into sachhafte Werte (thing-values) and gedankenhafte Werte (thought-values); that “experience in the broad sense” includes the latter; that “complete experience” is identified with the principal co-ordination (Bemerkungen). In short, you pay your money and take your choice. “Experience” embraces both the materialist and the idealist line in philosophy and sanctifies the muddling of them. But while our Machians confidingly accept “pure experience” as pure coin of the realm, in philosophical literature the representatives of the various trends are alike in pointing to Avenarius’ abuse of this concept. “What pure experience is,” A. Riehl writes, “remains vague with Avenarius, and his explanation that ‘pure experience is experience to which nothing is admixed that is not in its turn experience’ obviously revolves in a circle” (Systematische Philosophie [Systematic Philosopby], Leipzig, 1907, S. 102). Pure experience for Avenarius, writes Wundt, is at times any kind of fantasy, and at others, a predication with the character of “corporeality” (Philosophische Studien, XIII. Band, S. 92-93). Avenarius stretches the concept experience (S. 382). “On the precise definition of the terms experience and pure experience,” writes Cauwelaert, “depends the meaning of the whole of this philosophy. Avenarius does not give a precise definition” (Revue néo-scolastique, fevrier 1907, p. 61). “The vagueness of the term ‘experience’ stands him in good stead, and so in the end Avenarius falls back on the timeworn argument of subjective idealism” (under the pretence of combating it), says Norman Smith (Mind, Vol. XV, p. 29).
“I openly declare that the inner sense, the soul of my philosophy consists in this that a human being possesses nothing save experience; a human being comes to everything to which he comes only through experience. . . .” A zealous philosopher of pure experience, is he not? The author of these words is the subjective idealist Fichte (Sonnenklarer Bericht, usw., S. 12). We know from the history of philosophy that the interpretation of the concept experience divided the classical materialists from the idealists. Today professorial philosophy of all shades disguises its reactionary nature by declaiming on the subject of “experience.” All the immanentists fall back on experience. In the preface to the second edition of his Knowledge and Error, Mach praises a book by Professor Wilhelm Jerusalem in which we read: “The acceptance of a divine original being is not contradictory to experience” (Der kritische Idealismus und die reine Logik [Critical Idealism and Pure Logic], S. 222).
One can only commiserate with people who believed Avenarius and Co. that the “obsolete” distinction between materialism and idealism can be surmounted by the word “experience.” When Valentinov and Yushkevich accuse Bogdanov, who departed somewhat from pure Machism, of abusing the word experience, these gentlemen are only betraying their ignorance. Bogdanov is “not guilty” in this case; he only slavishly borrowed the muddle of Mach and Avenarius. When Bogdanov says that “consciousness and immediate mental experience are identical concepts” (Empirio-Monism, Bk. II, p. 53) while matter is “not experience” but “the unknown which evokes everything known” (Empirio-Monism, Bk. III, p. xiii), he is interpreting experience idealistically. And, of course, he is not the firstnor the last to build petty idealist systems on the word experience. When he replies to the reactionary philosophers by declaring that attempts to transcend the boundaries of experience lead in fact “only to empty abstractions and contradictory images, all the elements of which have nevertheless been taken from experience” (Bk. I, p. 48), he is drawing a contrast between the empty abstractions of the human mind and that which exists outside of man and independently of his mind, in other words, he is interpreting experience as a materialist.
Similarly, even Mach, although he makes idealism his starting point (bodies are complexes of sensations or “elements") frequently strays into a materialist interpretation of the word experience. “We must not philosophise out of ourselves (nicht aus uns herausphilosophieren), but must take from experience,” he says in the Mechanik (3rd Germ. ed., 1897, p. 14). Here a contrast is drawn between experience and philosophising out of ourselves, in other words, experience is regarded as something objective, something given to man from the outside; it is interpreted materialistically. Here is another example: “What we observe in nature is imprinted, although uncomprehended and unanalysed, upon our ideas, which, then, in their most general and strongest (stärksten) features imitate (nachahmen) the processes of nature. In these experiences we possess a treasure-store (Schatz) which is ever to hand. . .” (op. cit., p. 27). Here nature is taken as primary and sensation and experience as products. Had Mach consistently adhered to this point of view in the fundamental questions of epistemology, he would have spared humanity many foolish idealist “complexes.” A third example: “The close connection of thought and experience creates modern natural science. Experience gives rise to a thought. The latter is further elaborated and is again compared with experience” (Erkenntnis und Irrtum, S. 200). Mach’s special “philosophy” is here thrown overboard, and the author instinctively accepts the customary standpoint of the scientists, who regard experience materialistically.
To summarise: the word “experience,” on which the Machians build their systems, has long been serving as a shield for idealist systems, and is now serving Avenarius and Co. in eclectically passing to and fro between the idealist position and the materialist position. The various “definitions” of this concept are only expressions of those two fundamental lines in philosophy which were so strikingly revealed by Engels.
 THIS FOOTNOTE has been moved into BODY OF DOCUMENT.
 Revue de philosophic (Review of Philosophy)—a French idealist journal founded by E. Peillaubt, which was published in Paris from 1900 to 1939.