 Hempel’s most important contributions to the theory of science have been a series of explications of the structure of scientific explanations. His methodology was such that, following the preliminary examination of the linguistic and physical phenomena under consideration, he would advance a semi-formal characterization, one which he would subsequently subject to formal characterization using the resources of symbolic logic. The overarching theme of his work was the conception of explanation by subsumption, where specific events are subsumed by corresponding laws (of physics, of chemistry, of biology, and so forth). The conception of explanation by subsumption is rather ancient in its lineage, but Hempel advanced explicit formulations that drew distinctions between explanations of different kinds, especially those that invoke universal (or deterministic) laws, statistical (or probabilistic) laws, and the explanation of laws by means of theories.