The author defends (what he refers to as) "intensional realism" against sophisticated forms of instrumentalism, first, by elaborating a dispositional ontology for the physical world; second, by determining the necessary and sufficient conditions for the adequacy of scientific explanations; and third, by explicating the conception of scientific knowledge which is supported by this analysis. this work presents an alternative conceptual framework for understanding science which bears important affinites to the views of hacking, popper, and peirce.