Week 1 (MT 2026), 15 October

Ian Campbell (Heidelberg University): 'Aristotle's Defense of the Excluded Middle' 

Chair: Ed Lamb

Abstract: I offer a new interpretation of Aristotle’s first argument in defense of the principle of the excluded middle (PEM) in Metaphysics Γ.7 (1011b23­–29). Scholars have typically treated the passage as an attempt to derive PEM based on Aristotle’s canonical definitions of truth and falsity. Against this reading, I argue that this argument conforms to the strategy of an ‘elenctic demonstration.’ Its aim is not to establish PEM, but to show the impossibility of meaningfully denying it. On this interpretation, Aristotle maintains that any denial of PEM would have to take the form of a statement with determinate meaning. Yet such a statement already presupposes accounts of truth and falsity that entail an instance of PEM. Conversely, if one attempts to avoid these commitments in order to deny PEM consistently, one thereby refrains from meaningful assertion and fails to engage in a meaningful discussion. The result is a dilemma: either one asserts something meaningful and thereby presupposes PEM, or one avoids this presupposition but thereby fails meaningfully to deny it.