The provisional orientation, according to the convenient system of what are called factors, may, under given circumstances, be useful also to us who profess an altogether unitary principle of historic interpretation, if we do not wish simply to rest in the domain of theory, but wish to illustrate, through personal research, a definite period of history. As in that case we must proceed to direct and detailed research, we must first of all follow the groups of facts that seem pre-eminent, independent, or detached in the aspects of immediate experience. We should not imagine, in fact, that the unitary principle so well established, at which we have arrived in the general conception of history, may, like a talisman, act always and at first sight, as an infallible method of resolving into simple elements the immense area and the complicated gearing of society. The underlying economic structure, which determines all the rest, is not a simple mechanism whence emerge, as immediate, automatic and mechanical effects, institutions, laws, customs, thoughts, sentiments, ideologies. From this substructure to all the rest, the process of derivation and of mediation is very complicated, often subtile, tortuous and not always legible. The social organization is, as we already know, constantly unstable, although that does not seem evident to every one, except at the time when the instability enters upon that acute period which is called a revolution. This instability, with the constant struggles in the bosom of that same organized society, excludes the possibility for men coming to an agreement which might involve a new start at living an animal life. It is the antagonisms which are the principal cause of progress (Marx). But it is equally true, notwithstanding, that in this unstable organization, in which is given to us the inevitable form of domination and subjection, intelligence is always developed not only unequally, but quite imperfectly, incongruously and partially. There has been and there is still in society what we may call a hierarchy of intelligence, sentiments and conceptions. To suppose that men, always and in all cases, have had an approximately clear consciousness of their own situation, and of what was the most rational thing to do, is to suppose the improbable and, indeed, the unreal.