In this paper, I show that mathematicians can successfully engage in metaphysical debates by mathematical means. I present the contemporary work of Hugh Woodin and Peter Koellner. Woodin has argued for axiom-candidates which could, when added to our current set-theoretic axiom system, resolve the issue that some fundamental questions of set theory are formally unsolvable. The proposed method to choose between these axioms is to rely on future results in formal set theory. Koellner connects this to a contemporary metaphysical debate on the ontological nature of sets. I argue that Koellner connects mathematics to the philosophical debate in such a way that mathematicians can obtain a new philosophical argument by doing more mathematics. This story reveals an active connectedness between mathematics and philosophy.