In Metaphysics Theta 3 Aristotle attributes to the Megarics and unknown others a notorious modal thesis: (M) something can φ only if it is φ-ing. Aristotle does not tell us what motivated (M). Almost all scholars take Aristotle’s report to indicate that the Megarics defended (M) as a highly counterintuitive doctrine in modal metaphysics. But this reading faces several problems. First: what would motivate the Megarics to hold such a counterintuitive view? The existing literature tries, in various ways, to motivate (...) (M) in a way neither trivial nor absurd. But, as we will argue, the main approaches end up attributing an unsustainable position to the Megarics. Second: most historical evidence for the Megaric lineage presents the group’s philosophical practice as dialectical or negative. So why think that the claim reported in Theta 3 presents a positive, and highly controversial, metaphysical claim? This paper addresses these problems by proposing a dialectical (or negative) reading of the Megarics in Theta 3. By ‘dialectical’ we here mean a mode of philosophizing that neither seeks to establish the truth or falsity of certain theses, nor takes a skeptical stance. There are different reasons why a philosopher might want to take up such a mode; in the case of the Megarics we argue that they might have wanted to put pressure on Aristotle’s idea of possibility and the ‘test’ for possibility that Aristotle mentions in several works. Reading, as we do, (M) as (part of) a paradox about possibility and actuality, we argue that the Megarics’ dialectical approach here aims to highlight a shortcoming of an intuitive conception of possibility, which underpins Aristotle’s idea of possibility and which features in his test for possibility. (shrink)