Both Comte and Karl Marx set out to develop scientifically justified systems in the wake of European industrialization and secularization, informed by various key movements in the philosophies of history and science. Marx rejected Comtean positivism[29] but in attempting to develop a "science of society" nevertheless came to be recognized as a founder of sociology as the word gained wider meaning. For Isaiah Berlin, even though Marx did not consider himself to be a sociologist, he may be regarded as the "true father" of modern sociology, "in so far as anyone can claim the title."[30]: 130 
To have given clear and unified answers in familiar empirical terms to those theoretical questions which most occupied men's minds at the time, and to have deduced from them clear practical directives without creating obviously artificial links between the two, was the principal achievement of Marx's theory. The sociological treatment of historical and moral problems, which Comte and after him, Spencer and Taine, had discussed and mapped, became a precise and concrete study only when the attack of militant Marxism made its conclusions a burning issue, and so made the search for evidence more zealous and the attention to method more intense.[