Ideas and opinions are not spontaneously 'born' in each individual brain: they have had a centre of formation, or irradiation, of dissemination, of persuasion-a group of men, or a single individual even, which has developed them and presented them in the political form of current reality.

The principle must always rule that ideas are not born of other ideas, philosophies of other philosophies; they are a continually renewed expression of real historical development. The unity of history (what the idealists call unity of the spirit) is not a presupposition, but a continuously developing process.