When one takes a long look at the concept (or concepts) of scientific explanation, it is possible and plausible to distinguish three fundamental philosophical views. These might be called the epistemic, modal, and ontic. They can be discerned in Aristotle's Posterior Analytics and they are conspicuous in the twentieth-century literature. In its classic form—the inferential version—the epistemic conception takes scientific explanations to be arguments. During the period of almost four decades since the publication of the landmark Hempel-Oppenheim article, “Studies in the Logic of Explanation” (1948), the chairman of this symposium (Carl G. Hempel) has done more than anyone else to articulate, elaborate, and defend this basic conception and the familiar models that give it substance (Hempel 1965), though it has, of course, had many other champions as well. According to the modal conception, scientific explanations do their jobs by showing that what did happen had to happen.