Let us begin with the first question. Truly a difficult one, and offering a multiplicity of difficulties. The first of these arises so to speak, from the _nature of the sources_. The doctrine of historical materialism is not embodied in a classical and definite book by those authors, with whom it is as it were identified; so that, to discuss that book and to discuss the doctrine might seem all one thing. On the contrary it is scattered through a series of writings, composed in the course of half a century, at long intervals, where only the most casual mention is made of it, and where it is sometimes merely understood or implied. Anyone who desired to reconcile all the forms with which Marx's and Engels have endowed it, would stumble upon contradictory expressions, which would make it impossible for the careful and methodical interpreter to decide what, on the whole, historical materialism meant for them. Another difficulty arises in regard to the weight to be attached to their expressions. I do not think that there has yet been a study of what might be called Marx's _forma mentis_; with which Engels had something in common, partly owing to congeniality, partly owing to imitation or influence. Marx, as has been already remarked, had a kind of abhorrence for researches of purely scholastic interest. Eager for knowledge of _things_ (I say, of concrete and individual things) he attached little weight to discussions of _concepts_ and the _forms of concepts_; this sometimes degenerated into an exaggeration in his own concepts. Thus we find in him a curious opposition between statements which, interpreted strictly, are erroneous; and yet appear to us, and indeed are, loaded and pregnant with truth. Marx was addicted, in short, to a kind of _concrete logic_.[40] Is it best then to interpret his expressions literally, running the risk of giving them a meaning different from what they actually bore in the writer's inmost thoughts? Or is it best to interpret them broadly, running the opposite risk of giving them a meaning, theoretically perhaps more acceptable, but historically less true?