Aristotle

Plato's student for twenty years, and the first serious refusal of the whole picture. He agreed that knowledge is of the universal and denied that universals stand apart in a separate realm: the form of a thing is in the thing, and you find it by looking at octopuses and constitutions and rainfall, patiently, from inside the cave.

The honest opposition, kept in the room. Every door on this bench should hold the strongest argument against its own subject, and here it is: perhaps there is no outside. Perhaps the shadows are all there is to study, and studying them carefully is the whole of what can be done.