There is no doubt at all that the issue of determinism versus indeterminism was a central, dominating theme of Popper’s thought. By his own account he saw his criticism of the thesis of determinism as crucial to his defence not only of the reality of human freedom, moral responsibility and creativity but also as equally fundamental to his account of human rationality and to his theory of the content and growth of science as an objective, rational and most importantly demonstrably rational enterprise. Consequently a great deal of his writings discussing both the content and methodology of the natural and the social sciences alternately bear upon and presuppose his defence of indeterminism.