On what Ontology Is and not-Is

In this paper I study the connection between logic and metaphysics in Plato's participation theory, from the structural properties of the latter. Although Plato was the first ever to formulate the contradiction principle explicitly (in the Phaedo), the logic underlying his system appears to be paraconsistent. This confirms an earlier suggestion by G. Priest. Its technical characteristics and the textual evidence supporting this interpretation are both studied in detail.