An idea · Classical Greek · first attested 380 BCE
The Forms
Eternal, perfect originals of which everything in this world is a copy.
For Plato, the Triangle of geometry is not the triangle you draw – your drawing is approximate and smudged, while the Triangle is exact and eternal. Beauty itself, Justice itself, Equality itself, the Good itself: these exist independently of any beautiful, just, or good particular. To know is to grasp the Form. The whole project of Western metaphysics has been arguing with this idea – extending it, denying it, inverting it, secularizing it.