Abstract

In Book IV of the Metaphysics Aristotle argues that first philosophy investigates not only being qua being but also the axioms or principles of demonstration. In the same place he establishes which principles are first. The first among these is the principle of contradiction. The thesis I defend in my communication is that the principle of contradiction in Aristotle is not merely formal in the style of modern symbolic logic, but is the constituent law of all discourse. As such, the most precise sense in which it is a 'first principle' is that of a condition of the possibility of significance: terms and judgments have significance if they comply with the condition; if they violate it they signify nothing and are vacuous. If my interpretation is correct, various consequences will be derivable from a first principle, of which the most important is its link with essence and substance.