Geach, Aristotle and Predicate Logics

Abstract

AbstractGeach's account of the Aristotelian logic of categorical sentences supplemented the views shared by Frege, Russell, Quine and others. I argue that this particular predicate logic approach and Geach's points apply to only one variety of natural language categorical sentences. For example, it takes the universal categorical as a universal conditional “If anything is a man, then it is mortal”. A different natural language form can and should be invoked: “Every man is a mortal.” Employing special restricted quantifiers in a version of predicate logic, we justify a full square of opposition and the rules of quality and quantity that Geach rejected.