The Forms

The Forms (or Ideas) are the heart of Plato's metaphysics: eternal, changeless, perfect realities of which the things we perceive are imperfect, shifting copies. There is a Form of Beauty itself, of Justice itself, of Equality itself — and beautiful, just, or equal things are such only by participating in them. The Forms are grasped by intellect, not the senses, and they alone are fully real, while the sensible world hovers between being and not-being.

The arguments for them

Plato approaches the Forms from several directions. From perception: the many equal sticks fall short of, yet remind us of, Equality itself, which is not identical with any of them. From language and knowledge: definitions and genuine knowledge require stable objects that the flux of particulars cannot supply. And from recollection: the soul's ability to recognize that sensible things fall short implies a prior acquaintance with the perfect originals.

Plato's own doubts

Plato did not treat the theory as settled. In the Parmenides he raised hard objections against it — how can many things share one Form without it being divided? does explaining the many by a Form not generate an endless regress of further Forms (the 'third man')? — objections he left standing as a challenge.

In the later tradition

The Middle Platonists and Neoplatonists relocated the Forms within the divine Intellect, treating them as the thoughts by which the cosmos is patterned and the Demiurge works, crowned by the Good. Proclus worked out an elaborate theory of how the unparticipated Form gives rise to the shared character without being divided — the tradition's most refined answer to Plato's own puzzles.