Engels' conception of Marx's project was Marxism for the members of the Second International. When Engels said at Marx's graveside that ‘just as Darwin discovered the law of development of organic nature, so Marx discovered the law of development of human history’, he expected to be, and was, taken seriously. The rest of his life was dedicated to defending Marxism as a positivist social science. Such a Marxism, however, soon came under attack from some of the founders of the academic discipline of sociology: Durkheim, Pareto, Mosca, and Weber. These ‘academic critics’ rejected the claims of Marxism to scientific status, and questioned whether socialism would be as liberal democratic as capitalism. In the context of this sustained intellectual attack upon Marxism, and of the consolidation of liberal democratic regimes in some of the advanced countries of Western Europe, Eduard Bernstein, a leading theoretician of the SPD and, with Karl Kautsky, Engels' literary executor, sought to provide socialism with a foundation different from Marxism, and to assure the sceptics of socialism's liberal democratic intentions. The position he developed and defended is known as ‘Revisionism’. It was based on the contrast between the gradual transformation of existing society through reforms and a violent break in continuity between the existing society and socialism. Bernstein's ‘transition period’, although he never employed the concept, was the present; but his opponents within the SPD objected that real advances towards socialism could only be made after the socialist revolution.