Marx famously said that all criticism begins with the criticism of religion. This is often taken to be the starting point of a position that ends with the slogan that "religion is the opium of the people". However, as with most thinkers, this reduction to slogans does not do the ideas behind them justice. The critique of religion as a social phenomenon did not connote a dismissal of the issues behind it. Marx precedes the famous line in his Critique of Hegel's Philosophy of Right with the contention that religion was the "sigh of the oppressed creature in a hostile world, the heart of a heartless world and the soul of soulless conditions" and that an understanding of religion has to go hand in hand with an understanding of the social conditions that gave rise to it.

The description of religion as the heart of a heartless world thus becomes a critique not of religion per se but of the world as it exists. What this shows is that his consideration of religion, politics, economics and society as a whole was not merely a philosophical exercise, but an active attempt to change the world, to help it find a new heart. "The philosophers have only interpreted the world in various ways; the point is to change it," he wrote in his famous 11th thesis on Feuerbach, the phrase carved on his gravestone in Highgate cemetery.

Even though understanding and action were tightly linked in Marx, we can trace his understanding back separately, through two German earlier philosophers, Hegel and Feuerbach.

In Hegel he finds the concept of the idealistic dialectic as a means of understanding historical change but he uses Feuerbach's materialism as a tool for understanding it correctly. That's why he called his system dialectical materialism.

Hegel's dialectic is not at all materialistic. It is based on the existence and importance of ideas, which are conceived of as almost independent of the people who have them. We are merely their puppets. It was essentially an attempt to explain change in history during the period of revolutionary upheaval around the French revolution. Why do revolutions happen, he asks, and what happens to them? Why do things not stay the same and why is some world spirit (Weltgeist) constantly changing its mind about the way it wants the world to be and introducing a new "spirit of the age" (Zeitgeist)? Taking his cue from Kant, adding in some Spinoza and a dash of neo-Platonism, Hegel maintained that change happened in the world because it was immanent in a growing development towards something as yet incomplete but which had at its core the unfolding of the idea of human freedom. History thus became simply a vessel for this unfolding, a totality which was constantly changing and completing itself through a series of constructive negations.

The dialectic is a theory of motion which posits that within every given situation there exists its own negation. The tension and interplay between the situation and its negation, produce constantly new and emergent forms of social existence. Of course there are difficulties in deciding what exactly is the negation of any particular situation. I will deal with those later.

Marx took this Hegelian and idealistic dialectical approach and added in a materialist grounding from Feuerbach who was in many ways a sort of political Ditchkins of his day. For him religion "poisons, nay destroys, the most divine feeling in man, the sense of truth". His insight was that all forms of religious expression were merely the abstracted vague longings of the human species translated into deities and their hangers-on, or in other words a god delusion.

Marx's real synthesis of the debate between Hegel and Feuerbach is to agree with both of them but to turn them both upside down (or back on their feet as he would have it) and locate their ideas in concrete historical situations. Hegel's idealism and Feuerbach's materialism had one thing in common and that was their abstraction from real concrete conditions. Hegel's dialectic was indeed a way of understanding change in the world but it failed to recognise that change emanated from prevailing material conditions rather than from the workings of the Weltgeist. On the other hand Feuerbach's materialism dealt only in abstract form with the way people perceived religion and did not locate the form that abstraction took in the way that people, above all classes, interacted with each other historically.

By 1848 Marx was thus able to open the Communist Manifesto with the contention that "the history of all hitherto existing society is the history of class struggles". This, for Marx, was the real motor of history; real struggles between real classes which produced real historical outcomes which in turn went on to become new struggles as the process of the negation of the negation – "the old mole" as Marx called it – carried on burrowing away, all the time throwing up new ways of thinking which themselves went on to negate and change the world.

What I shall do in coming weeks is to look at how all of this actually works, how Marxists took up the baton and what the consequences of it all were. I shall also ask whether Marxism still has any explanatory power today, in a new age of revolutionary upheaval, or whether we have, in Hegel's and Fukuyama's terms, reached The End of History.