— Henri Lefebvre French philosopher 1901 - 1991
Context: The method of Marx and Engels consists precisely in a search for the link which exists between what men think, desire, say and believe for themselves and what they are, what they do. This link always exists. It can be explored in two directions. On the one hand, the historian or the man of action can proceed from ideas to men, from consciousness to being - i. e. towards practical, everyday reality - bringing the two into confrontation and thereby achieving archieving criticism of ideas by action and realities. That is the direction which Marx and Engels nearly always followed in everything they wrote; and it is the direction which critical and constructive method must follow initially if it is to take a demonstrable shape and achieve results.
But it is equally possible to follow this link in another direction, taking real life as the point of departure in an investigation of how the ideas which express it and the forms of consciousness which reflect it emerge. The link, or rather the network of links between the two poles will prove to be complex. It must be unravelled, the thread must be carefully followed. In this way we can arrive at a criticism of life by ideas which in a sense extends and completes the first procedure.