As we now turn to this theory itself and its significance for the social movement we are obliged, I think, to concede that the entrance of Karl Marx was a decisive turning-point in this agitation, because through him it was based upon a fundamentally changed conception of history and humanity. This change is occasioned by the fact that, in place of an idealistic, or rather partisan, way of looking at things, a realistic vision obtains, and thus for the social movement the idea of "revolution" passes into the thought of "evolution." The spirit of the nineteenth century supplants the spirit of the preceding centuries. You remember how I sought to make clear to you the essence of this spirit in connection with the teachings of the utopists; if I may be allowed to refer to it again, it is that idealistic conception of man and life,[1] cherished now only by the scholars, that faith in humanity as good by nature, that belief that men so long as they are not led astray by the mistake or malice of individual bad men will live in the most affectionate peace with their brethren; it is that belief in a "natural order" of the past and future--that rock-fast confidence that only explanation and exhortation are needed in order to bring men out of this vale of tears to the happy islands of the blest. This is that faith in the power of eternal love which through its own force shall overcome the bad, and help the good to victory. This it was that, though the leaders were not conscious of it, really lay at the bottom of all political and social agitation until the middle of our century; this it is that, in my opinion, as I have already said, still slumbers in the lap of anarchism, even to-day as an instinct. This fundamental tendency is now directly reversed; the belief in a humanity good by nature gives place to the conviction that man is of himself ruled by no noble motives, that he carries within himself the _bête humaine_ even in all culture and in spite of all "advance." Hence the conclusion: that a man, in order to accomplish anything in the world, must before all call upon "interest"--a normal and material instinct. For it is the most important conclusion for the fate of the social movement, that now "interest" rules in the world; that where anything is to be done, or a class, like the proletariat, is to be emancipated, a man needs some weapon stronger than the theory of "eternal love" against the interest of the capitalist class, and must present force against force, might armed by "interest." At the end of all thought upon this matter lies this consideration, which leads not only to the theory, but as well to the practice, of class strife. Combat is the solution of the difficulty for this hard and unlovely proletarian generation which has grown up since the middle of our century; not peace, not reconciliation, not a general brotherhood--but battle. That this strife is no longer open warfare,