The standard empiricist conception of theory evaluation regards our judgment of the epistemic quality of a theory to be a matter of applying rules of method to the theory and the evidence. Kuhn’s contrasting view is that we judge the quality of a theory (and its treatment of the evidence) by comparing it to a paradigmatic theory. The standards of assessment therefore are not permanent, theory-independent rules. They are not rules, because they involve perceived relations of similarity (of puzzle-solution to a paradigm). They are not theory-independent, since they involve comparison to a (paradigm) theory. They are not permanent, since the paradigm may change in a scientific revolution. For example, to many in the seventeenth century, Newton’s account of gravitation, involving action at a distance with no underlying explanation, seemed a poor account, in that respect at least, when compared, for example, to Ptolemy’s explanation of the motion of the planets in terms of contiguous crystalline spheres or to Descartes’ explanation in terms of vortices. However, later, once Newton’s theory had become accepted and the paradigm by which later theories were judged, the lack of an underlying mechanism for a fundamental force was regarded as no objection, as, for example, in the case of Coulomb’s law of electrostatic attraction. Indeed, in the latter case the very similarity of Coulomb’s equation to Newton’s was taken to be in its favour.