Scientism is a philosophy which purports to define what the world ‘really is’. It adopts what the philosopher Thomas Nagel called ‘an epistemological criterion of reality’, defining what is real as that which can be discovered by certain quite specific methods of investigation. As a consequence all features of experience not revealed by those methods are deemed ‘subjective’ in a way that suggests they are either not real, or lie beyond the scope of meaningful rational inquiry. This devalues capacities that (...) (we argue) are in fact essential components of good reasoning and virtuous practice. Ultimately, the implications of scientism for statements of value undermine value-judgements essential for science itself to have a sound basis. Scientism has implications, therefore, for ontology, epistemology and also for which claims we can assert as objective truths about the world. Adopting scientism as a world view will have consequences for reasoning and decision-making in clinical and other contexts. We analyse the implications of this approach and conclude that we need to reject scientism if we are to avoid stifling virtuous practice and to develop richer conceptions of human reasoning. (shrink)