 The first principle reflects the sense in which universal quantification is transitive. The second principle captures the idea that the universal premise can license replacement of ‘S’ with ‘P’ in a proposition about some individual. In this sense, classical logic exhibits a striking unity and simplicity, at least with regard to inferences involving the Aristotelian quantifiers and predication. For further discussion, see Sommers (1984), van Bentham (1986), Sanchez (1991, 1994), and Ludlow (2005).