ABSTRACT
This chapter discusses the semantics of term negation and the validity of obversion from Aristotle’s perspective. It asks which overall semantics for Aristotle’s assertoric syllogistic fits best what he says about term negation and obversion in De Interpretatione 10 and Prior Analytics I 46. Term negation is the operation whereby one builds negative terms, like “not-blue” or “not-bird”, which can feature as subject or predicate in a categorical proposition. In those texts, Aristotle considers the possibility of extending his assertoric logic to include also negative terms. Obversion is a form of inference in this extended logic whereby one goes from affirmation to negation or vice versa just by changing the predicate of the proposition from positive to negative or vice versa. For example, from “Every bird is blue”, one may infer by obversion “No bird is not-blue”. Aristotle accepts the obversion of affirmations as valid but rejects it for negations. This essay tries to find out why. It argues against the prevailing view, which accounts for negative terms in terms of restricted complements, and against an alternative account in terms of mereological complements. The answer defended relies on the view that for Aristotle negations have no existential import while affirmations do.
