First, it is evident that in the domain of historico-social determinism, the linking of causes to effects, of conditions to the things conditioned, of antecedents to consequents, is never evident at first sight in the subjective determinism of individual psychology. In this last domain it was a relatively easy thing for abstract and formal philosophy to discover, passing above all the baubles of fatalism and free will, the evidence of the motive in every volition, because, in fine, there is no wish without its determining motive. But beneath the motives and the wish there is the genesis of both, and to reconstruct this genesis we must leave the closed field of consciousness to arrive at the analysis of the simple necessities, which, on the one side, are derived from social conditions, and on the other side are lost in the obscure background of organic dispositions, in ancestry and in atavism. It is not otherwise with historical determinism, where, in the same way, we begin with motives religious, political, aesthetic, passionate, etc., but where we must subsequently discover the causes of these motives in the material conditions underlying them. Now the study of these conditions should be so specified that we may perceive indubitably not only what are the causes, but again by what mediations they arrive at that form which reveals them to the consciousness as motives whose origin is often obliterated. And thence follows indubitably this second consequence that in our doctrine we have not to re-translate into economic categories all the complex manifestations of history, but only to explain in the _last analysis_ (Engels) all the historic facts _by means of the underlying economic structure_ (Marx), which necessitates analysis and reduction and then interlinking and construction.