Ignorance is commonly assumed to be a lack of knowledge in Plato’s Socratic dialogues. I challenge that assumption. In the Protagoras, ignorance is conceived to be a substantive, structural psychic flaw—the soul’s domination by inferior elements that are by nature fit to be ruled. Ignorant people are characterized by both false beliefs about evaluative matters in specific situations and an enduring deception about their own psychic conditions. On my interpretation, akrasia, moral vices, and epistemic vices are products or forms of ignorance, and a person who lacks knowledge is not necessarily ignorant.