sense data; sense-reference; Seth Pringle-Pattison Andrew; Sextus Empiricus; Shaftesbury - Third Earl of - Anthony Ashley Cooper; Sidgwick Henry; Siger of Brabant; simpliciter; simplification; sine qua non; Singer Peter; singular proposition; Sinn - Bedeutung; skepticism; Skinner Burrhus Frederic; Smart John Jameison Carswell; Smith Adam; social contract theory; stroke function;