Analytic moral philosophy's strong divide between empirical and normative restricts facts to providing information for the application of norms and does not allow them to confront or challenge norms. So any genuine attempt to incorporate experience and empirical research into bioethics – to give the empirical more than the status of mere ‘descriptive ethics’– must make a sharp break with the kind of analytic moral philosophy that has dominated contemporary bioethics. Examples from bioethics and science are used to illustrate the problems with the method of application that philosophically prevails in both domains and with the conception of rationality that underlies this method. Cues from how these problems can be handled in science then introduce summaries of richer, more productive naturalist and constructivist accounts of reason and normative knowledge. Liberated by a naturalist approach to ethics and an enlarged conception of rationality, empirical work can be recognized not just as essential to bioethics but also as contributing to normative knowledge.