Has the emergence of post-positivism in philosophy of science changed the terms of the “is/ought” dichotomy? If it has demonstrated convincingly that there are no “facts” apart from the theoretical frames and evaluative standards constructing them, can such a cordon sanitaire really be upheld between “facts” and values? The point I wish to stress is that philosophy of science has had a central role in constituting and imposing the fact/value dichotomy and a revolution in the philosophy of science should not leave the dichotomy unaffected. The connection between post-positivism and naturalism will be my guiding thread in considering this “last dogma of positivism.” First this essay will specify the sense of naturalism that it will take to be essential to the post-positivist philosophy of science: the deflation of the notion of the “purity” of scientific knowledge. Then it will turn to the question of the implications that follow for the “autonomy” of ethics, including the danger posed by a new form of scientistic reductionism.