The Socrates of the early dialogues devotes his attention to the search for definitions of morally significant forms, but never asks after the fundamental ontological and epistemological status of these entities. For example, Socrates asks Euthyphro to provide him with a definition of piety (Euthyphro 5d), Charmides to provide him with a definition of temperance (Charmides 159a), and both Nicias and Laches to provide him with a definition of courage (Laches 190d–e). In all these cases, what Socrates asks his interlocutors to define is something he calls a “form,” namely whatever it is by virtue of which persons and actions are pious, temperate, or courageous. Although Socrates reveals that he has opinions about what some of these forms are like and about what all forms must be like, he never suggests that these opinions rise to the level of knowledge. More importantly, he never so much as speculates about whether forms are or are not the sorts of things that can be perceived by means of the senses, whether they have parts or are indivisible wholes, whether they are eternal and indestructible or whether they come to be or perish, whether they can undergo any sort of change (whether in the form of translation, rotation, or alteration), whether they are perfect or in some way deficient, or whether they are such as to be humanly knowable.

It is in the dialogues of the middle period, principally the Phaedo and the Republic, that Plato begins to ask and answer these questions.