Evidence-based practice (EBP) has become a critical concept for ethical, accountable professional nursing practice. However, critical analysis of the concept suggests that EBP overemphasizes the value of scientific evidence while underplaying the role of clinical judgement and individual nursing expertise. This paper explores the empiricist position that valid evidence is the basis for all knowledge claims. We argue against the positivist idea that science should be regarded as the only credible means for generating evidence on which to base knowledge claims. We propose that the process of critically reflecting on evidence is a fundamental feature of empirical epistemology. We suggest that critical reflection on evidence derived from science, arts and humanities and, in particular, nursing practice experience can provide a sound basis for knowledge claims. While we do not attempt to define what counts as evidence, it is argued that there is much to be gained by making the processes of critical reflection explicit, and that it can make a valid contribution to expert nursing practice, without recourse to irreducible concepts such as intuition.