This paper offers a critique of Fawcett's paper ‘Conceptual models and nursing practice the reciprocal relationship’ published in 1992, in which it is argued that ‘conceptual models inform and transform nursing practice by informing and transforming the way in which nursing is experienced and understood, and that nursing practice informs and transforms conceptual models by informing and transforming the content of the conceptual model’ The critique begins by locating Fawcett's view of the relationship of nursing models to nursing practice within the intellectual tradition of positivism For the purposes of the critique, Fawcett's positivism is not taken as being problematic in itself, however, it is argued that the standards of evidence upon which some of her arguments are based are not compatible with the practice of positivist social science, with the result that the paper is internally inconsistent In particular, Fawcett's suggestion that nursing models are validated as evidence accumulates in their favour is contrasted with Popper's view that the validity of theoretical statements is established as they withstand attempts to demonstrate their falsity, and Fawcett's belief that nursing models are models in the scientific sense, which can be inferred from her adoption of the terminology of Kuhnian epistemology, is not found to be justified If, for the positivist, the validity of practice is directly proportional to the validity of the theory upon which it is based, then nursing models which lack ‘scientific’ validity cannot be regarded as a proper basis for nursing practice Finally, Fawcett has been criticized for failing to produce evidence of any kind to demonstrate that nursing models have a beneficial effect upon nursing outcomes