Any thoroughgoing physicalist is challenged to give an account of immaterial entities such as thoughts and mathematical objects. The Stoics, who eagerly affirmed that only bodies exist, crafted an elegant solution to this challenge: not everything that is Something (ti) exists. Rather, some things have a derivative mode of reality they call subsistence: these entities are non-existent in that they are not themselves solid bodies, but they are nonetheless Something physical because they depend on bodies for their subsistence. My dissertation uncovers the unifying principles of Stoic subsistence, and shows how they can account for thoughts and other immaterial entities without running afoul of their physicalist commitments.
While all commentators agree that the Stoics posited Something as the highest category of being, they have failed to find a coherent physicalist account of Stoic ontology. For instance, (1) a canonical set of incorporeals (time, place, void, and what is sayable (lekton)) is well attested, but there is little agreement as to what these entities have in common as incorporeals, which makes the category look like an ad hoc collection of left-over entities. (2) It is also contentious whether the Stoics recognized other non-existent Somethings besides the incorporeals, namely a third category of Somethings that are neither corporeal nor incorporeal. (3) Finally, many commentators take the Stoics to countenance an additional class of Not-Somethings between Something and nothing at all, rendering Something incoherent as highest and most comprehensive genus.
I argue first that the Stoics developed a criterion for subsistence that applies to all immaterial Somethings, admitting only objective particulars. Further, I show that the Stoics recognized not just one but two kinds of subsistence: one that defines the incorporeals as a class, and the other what is neither corporeal nor incorporeal. The incorporeals can all be seen as body-less: entities that depend on body without themselves being bodies, much as the flow of traffic depends on cars without being identical to the cars. They are immaterial but still physical; in modern parlance, one might say the Stoics take incorporeals to supervene on bodies.
How such a thesis can apply to the Sayables, or lekta (roughly, the meanings of our words) is an especially thorny issue (for the Stoics as for contemporary philosophers of mind). If lekta subsist according to rational impressions (logikai phantasiai), themselves mental and corporeal, it is not clear how these novel semantic entities get the objectivity they need to do their hefty dialectical duties. How can mind-dependent entities be the propositional content shared in communication, have logical properties and play the role of facts? I argue that the Stoics had on offer a certain doctrine of meaning as use that can address these challenges without running afoul of the principle of body-less subsistence that unifies the incorporeals as a category. Stoic incorporeals are thus not a mere ad hoc collection of left over entities (as impasse (1) above suggested), but a principled segment of reality.
What is neither corporeal nor incorporeal, which includes mathematical entities and creatures of fiction, is also a principled ontological category. Adducing broad textual evidence, I show that the Stoics recognized a mode of subsistence unique to products of thought, and that they categorized centaurs and points, for example, accordingly. Since the thoughts, texts and illustrations that give rise to such entities are themselves corporeal, the account remains true to their physicalist commitments. This second mode of subsistence, previously unnoticed by commentators, underwrites a comprehensive tripartite ontology, settling problems (2) and (3) above. The result is an elegant, modern-minded ontology with principled responses to problems that continue to engage physicalists today.
