Plato's thought evolves from the epistemology of the
Meno, Phaedo, and
Republic to the Combined Doctrine of the
Theaetetus. The Combined Doctrine maintains that both Forms and certain objects rooted in perception are objects of knowledge. Dialectic results in apprehension of the Good, and consequently of being, which brings about a permanent change in a person's state of mind enabling one to know what one previously believed. The Combined Doctrine resolves the paradoxes of the refutations of the
Theaetetus. It turns out that the difference between true belief and knowledge for Plato amounts to difference in states of mind.