Plato was much more concerned with what might be called truths of essence than with truths of fact. Truths of essence involve interpretation of meaning, and always have an implicit normative dimension. They are inseparably involved with questions of what is good or right. As Aristotle might say, they tell us what and why something is rather than merely “that” something is.
There is no general way to test whether we have completely grasped an essence, and not just what Hegel would call a one-sided view of it. As Brandom might say, all grasping of essences is defeasible. Plato makes his leading characters say many things that apply this in particular cases. Essences are the object of interpretation, not certain knowledge. (See also Dialogue; The Epistemic Modesty of Plato and Aristotle; Plato and Aristotle Were Inferentialists; Brandom on Truth; Foundations?)