PHYSICIANS may be startled to discover that they think in mathematical sets and with symbolic logic. The thinking occurs with every act of diagnosis, prognostic estimation, therapeutic decision and clinical correlation with laboratory data. These acts are really exercises in deductive and inductive reasoning, and can be described in appropriate mathematical symbols and diagrams.The branches of mathematics (or philosophy) used for these functions are called set theory and symbolic logic; they are about a century old. As relatively new mathematical developments, they were not included in the premedical training of most contemporary physicians. Courses in these disciplines, however, have . . .