I have always discussed frankly the views expressed in the writings of my eminent friend Professor Antonio Labriola. I am therefore glad that he has taken the same liberty with me, and has subjected to a vigorous criticism (in the French edition of his book on _Socialismo e la filosofia_),[74] my interpretation of the Marxian theory of value.[75] Labriola has been impelled to this also from a wish to prevent my opinions from appearing, 'to the reader's eyes,' as a supplement, approved by him, of his own personal ones. And though I do not think that 'to the reader's eyes' (I will however add _intelligent_ readers), this would be possible, since, I have always carefully indicated the points, and they are neither few nor unimportant, where we disagree: yet being convinced that clearness is never superfluous, I welcome his intention to make it still plainer that I am not he, and that he thinks with his mind whilst I think with mine. Labriola rejects entirely the method adopted by me, which he describes variously as _scholastic_, _metaphysical_, _metaphorical_, _abstract_, _formal logic_. When I take pains to point out the differences between _homo oeconomicus_ and man, moral or immoral, between personal interest and egoism,[76] he shrugs his shoulders, he does not refuse a certain indulgence to this _traditional scholasticism_, and compares me to the man in the street who speaks of the rising or setting of the sun, or of _shining light_ and _warm heat_. When I firmly maintain the theoretical necessity for a _general economics_ in addition to the heterogeneous considerations of sociological economics, he taxes me with creating, _in addition to all the visible and tangible animals, an animal as such_. And he charges me, moreover, with wishing to attack history, comparative philology and physiology in order to substitute for all these the plain _Logic_ of Port Royal, so that instead of studying examples of epigenesis which have actually occurred, such as the transitions from invertebrates to vertebrates, from primitive communism to private property in land, from undifferentiated roots to the systematic differentiation of nouns and verbs in the Ariosemitic group, it might suffice to register these facts in concepts passing from the more general to the more particular, in the series A a^1 a^2 a^3 etc.