ABSTRACT
Counterfactual reasoning is just as commonplace in scientific theory and practice as it is in our ordinary lives. Understanding the significance of such inferences requires paying close attention to the nature and foundations of conditionals, an important-albeit thorny-endeavor that philosophers of science typically (and happily) delegate to metaphysicians, philosophers of language, and linguists. This, I argue, is a mistake. The aim of this essay is to discuss the role of counterfactual reasoning in science, focusing specifically on molecular medicine. I suggest that subjunctive conditionals play a key part in the diagnosis and prognosis of molecular diseases and other pathological conditions. Yet, understanding the prominence of these sui generis statements in medical decision making requires some radical departures from traditional semantic analyses.
