Marx’s powerful critique has as it basis a unique approach to reality — the dialectic. Taking from G.W.F. Hegel. Marx believed that any study of reality must be attuned to the contradictions within society and, indeed, he sees contradiction as the motor of historical change. Unlike Hegel, Marx believed that these contradictions existed not simply in our minds (i.e., in the way we understand the world), but that they had a concrete material existence, hence dialectical materialism. According to Marx at the heart of capitalism was the contradiction between the demands of the capitalist to earn a profit and the demands of the worker, who wants to retain some profit to subsist. Over time, the workings of the capitalist system would exacerbate this contradiction, and its resolution can be had only through social change.
The dialectical approach suggested by Marx does not recognize the division between social values and social facts. To do so leads away from any real understanding of the problems people face. Additionally, the dialectical method does not envision the social world as being dominated by a cause-and-effect relationship; instead, it looks at the reciprocal relations among social factors within the totality of social life. These relations include not only contemporary phenomena but also the effects of history, as dialecticians are concerned with how the past shapes the present and how the present lays the seeds for the future. Because of this complex set of relations, which often fold back in on themselves, the future is both indeterminate and contingent on individual action. Indeed, this relationship between actors and structures is at the heart of Marx’s theory. Structures both constrain and enable individuals, having the potential of both helping them to fulfill themselves and contributing to their exploitation.
More summaries of Marx's writings and ideas:
An Extended Summary of The Communist Manifesto by Marx and Engels (chapter 1, chapter 2, chapters 3 and 4)