Research in cognitive psychology has been by and large dominated by attempts to explain how psychological processes can be explained as products of biological ones; these processes are presumed to be causal. These theories fail to account for and be integrated with theories of non-causal mental activities. In order to bridge this gap a new theory of mental processes is needed. Karl Popper and John Eccles’s three world theory offers a promising path. According to this view there are biological entities, rational thought processes and ideas’. It is a revision of a view that Popper adopted as a member and student of the Würzburg School, which held that there are biological entities, causal psychological processes and ideas’. By going back towards the original and redoing it as a four world theory, by adding to it non-causal rational thought processes, the unfortunate widespread influence of associationist psychology and inductivist methods may be overcome and new social aspects of cognitive psychology may be opened.