year each. In 1916, he was hired by Harvard as a philosophy professor, where he stayed until he retired in 1952. Scanlan (2000) is a study of Sheffer's life and work.

Sheffer proved in 1913 that Boolean algebra could be defined using a single primitive binary operation, "not both . . . and . . .", now abbreviated NAND, or its dual NOR, (in the sense of "neither . . . nor"). Likewise, the propositional calculus