The philosophy of science as initiated and developed in this century mainly by empiricists was purely systematic in its orientation. Increasing attention to the history of science and to the psychological and sociological aspects of its practice should have, one might have thus expected, meant a welcome addition to the logic of science. Whoever entertained such hopes was, however, in for a bitter disappointment. In particular, with the appearance of Professor Kuhn's work on scientific revolutions it became dreadfully clear that the results achieved in the different branches did not even yield a consistent overall picture of science. The fledgling student of the philosophy of science appeared to be faced with having to choose between two incompatible paradigms: the logical or the psychological-historical.