Aquinas's Metaphysics of Modality: A Reply to Leftow

Brian Leftow sets out to provide us with an account of Aquinas’s metaphysics of modality. Drawing on some important recent work, which is surely close to the spirit (if not quite the letter) of Aquinas’s thought, he frames his discussion in terms of “truthmakers”: what is it that makes true claims about possibility and necessity—that is to say, what serves as their ontological ground or ultimate metaphysical explanation? Leftow’s main thesis is that, for Aquinas, all true modal claims are made true by one and the same thing—namely, God. Along the way, however, he also attempts to show that Aquinas’s endorsement of this thesis commits him to an objectionable form of Platonism about possible worlds.