It was the aim of William Stanley Jevons (1835–1882), himself a pupil of De Morgan, to render Boole's calculus more simple and "logical" by removing those of its features that he found "mysterious" and by reducing its operations to mechanical routine. He also professed, officially, to reject the extensional standpoint in favor of a "pure logic" of terms, or "qualities," though the result in practice was still effectively a class or propositional logic, conceived rather in the manner of De Morgan's "onymatic" system. These views are set forth in two pamphlets, Pure Logic (London and New York, 1864) and The Substitution of Similars (London, 1869; both reprinted in Pure Logic and Other Minor Works, London, 1890), and at greater length in The Principles of Science (2nd ed., London, 1887) and Studies and Exercises in Deductive Logic (London, 1884).

Jevons takes over the Boolean notations for conjunction and identity (AB, A = B) and admits negative...