It is often assumed that: (a) in his early dialogues Plato uses the character of Socrates to present some of his own views concerning the search for definitions in ethics, and (b) starting with the middle dialogues Plato’s interests shift radically; in them he seems to be concerned with ontology, i.e. the theory of forms. Hence an exegetical puzzle arises: What exactly is the connection between the project of the early dialogues, the quest for Socratic definitions, and the emergence of the theory of Forms in the middle dialogues? In his early dialogues Plato often refers to what has come to be known as the “Principle of the Priority of Definitional Knowledge”. However, If we accept G. Matthews’ thesis that we ought to adopt an aporetic reading of the passages where this principle is referred to, the aforementioned exegetical problem can be readily resolved.