Any reader of Labriola's book who tries to obtain from it a precise concept of the new theory of history, will reach in the first instance a conclusion which must appear to him evident and incontestable, and which I sum up in the following statement: 'historical materialism, so-called, _is not a philosophy of history_.' Labriola does not state this denial explicitly; it may even be granted that, in words, he sometimes says exactly the opposite.[3] But, if I am not mistaken, the denial is contained implicitly in the restrictions which he places on the meaning of the theory. The philosophical reaction of realism overthrew the systems built up by teleology and metaphysical dogmatism, which had limited the field of the historian. The old philosophy of history was destroyed. And, as if in contempt and depreciation, the phrase, 'to construct a philosophy of history,' came to be used with the meaning: 'to construct a fanciful and artificial and perhaps prejudiced history.' It is true that of late books have begun to re-appear actually having as their title the 'philosophy of history.' This might seem to be a revival, but it is not. In fact their subject is a very different one. These recent productions do not aim at supplying a _new philosophy of history_, they simply offer _some philosophising about history_. The distinction deserves to be explained. The possibility of a philosophy of history presupposes the possibility of reducing the sequence of history to general concepts. Now, whilst it is possible to reduce to general concepts the particular factors of reality which appear in history and hence to construct a philosophy of morality or of law, of science or of art, and a general philosophy, it is not possible to work up into general concepts the single complex whole formed by these factors, _i.e._ the _concrete fact_, in which the historical sequence consists. To divide it into its factors is to destroy it, to annihilate it. In its complex totality, historical change is incapable of reduction except to one concept, that of _development_: a concept empty of everything that forms the peculiar content of history. The old philosophy of history regarded a conceptual working out of history as possible; either because by introducing the idea of God or of Providence, it read into the facts the aims of a divine intelligence; or because it treated the formal concept of development as including within itself, logically, the contingent determinations. The case of positivism is strange in that, being neither so boldly imaginative as to yield to the conceptions of teleology and rational philosophy, nor so strictly realistic and intellectually disciplined as to attack the error at its roots, it has halted halfway, _i.e._ at the actual concept of development and of evolution, and has announced the philosophy of evolution as the true philosophy of history: development itself--as the law which explains