Engels wrote this book to settle a debt, and he was forty years late paying it.

In 1845 he and Marx had shut themselves up in Brussels to write out, at length, what separated them from the German philosophy they had grown up in. The manuscript never found a printer; they left it "to the gnawing criticism of the mice all the more willingly as we had achieved our main purpose - self-clarification". Four decades passed. Marx died. Neither had ever gone back to Ludwig Feuerbach, the man whose influence on them during their period of storm and stress it was, Engels wrote, "an undischarged debt of honour" to acknowledge. Then the editors of Die Neue Zeit asked him for a review of a new book on Feuerbach by the Danish philosopher C. N. Starcke, and Engels wrote something much larger than a review.

The book is short, written at speed, and does the work of a much longer one. In four chapters it sets out what Hegel's system contained that was worth keeping and what had to be thrown away; states the great basic question of philosophy and why the answers divide philosophers into camps; takes Feuerbach's materialism apart, with particular attention to his ethics; and then sketches, in twenty pages, the materialist conception of history.

That last chapter is why the book outlived its occasion. Starcke is forgotten and Feuerbach is read mostly by specialists, but the account of how ideas about law, politics and religion arise on an economic basis and then acquire a life of their own is still being argued about. So is its central habit of mind: when an idea presents itself as obvious, ask what interest finds it obvious, and when it became so. Engels is emphatic that this is not cynicism about ideas - "everything which sets men in motion must go through their minds" - but a refusal to take the self-description of an age at face value.

New critical introduction by Dmitry Chasovennikov.