His personality, the characteristics of which were strikingly developed through the external circumstances of his life, was marked by extraordinary intellectual activity. He was a pitiless and positive critic in his very nature. He had an abnormally sharp vision for psychological and historical continuity, especially where these are based upon the less noble impulses of mankind. A word of Pierre Leroux's seems to me as if coined for Marx: "il etait ... fort pénétrant sur le mauvais côté de la nature humaine." So it was by nature easy for him to believe in Hegel's teaching that "evil" has accomplished all the development of mankind. His conception of the world is expressed in Wallenstein's magnificent words: "To the bad spirit belongs the earth, not to the good; the good things that the gods send to us from above are to be held only in communal possession. Their light gives us joy, yet makes no man rich; in their kingdom there is no private possession." What qualified Karl Marx to reach the first rank among the social philosophers of the nineteenth century, and to obtain next to Hegel and Darwin the greatest influence upon modern ideas, was the fact that he united a knowledge of the highest form of the historic philosophy of his time--Hegel--with a knowledge of the highest form of social life--that of Western Europe, of France, and especially of England. It was because he knew how to concentrate, as by a lens, all the rays of light which had been shed by other thinkers, and because he was able through his cosmopolitan experience to withdraw attention from the incidental features of national development, and to concentrate it upon what is typical in modern social life. Marx, in common with his friend Friedrich Engels, in a large number of monographs, the best known of which is _Capital_, has laid the ground-lines of an amazing system of social philosophy; but this is not the place for a study of its particular features. What interests us much more at this time is the Marxian theory of social agitation, because this is especially what has enabled him to influence decisively the progress of social development. In no single book of his is this theory comprehensively presented. Yet we find all the essential elements of it in the celebrated "Communistic Manifesto" of Marx and Engels in the year 1847, which was presented as a programme to the "League of the Righteous" in Brussels; they accepted it and thus changed themselves into a "League of Communists." The "Communistic Manifesto" contained the principles of a philosophy of history, upon which the programme of a party is based. Its leading thoughts are these: