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, smudged, finite, while the Triangle is exact, eternal, unchanging. Beauty itself, Justice 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, secularizing it.