According to Sir Karl Popper, there is a harmful approach to the social sciences called 'historicism'. This takes their principal aim to be historical prediction of an unconditional sort and the chief means to this the discovery of laws of historical development. The chief exemplar is held to be Marx. This paper distinguishes two possible sorts of laws of historical development. Popper's arguments against each are rejected. Which sort it is most plausible to ascribe to Marx is considered. Four models (...) of historical determinism are distinguished and the question of Marx's view or views on the question is discussed in terms of them. (shrink)