In his theory of the Forms, Plato argues that not only are the ideal versions of everyday entities real, but that they are more real than those entities themselves. The perceptual world, he believes, is not fully real nor fully unreal, but continually changing and ultimately unknowable. Only the unchanging Ideas are real and knowable, though the latter only with great effort. In Plato’s own words, from Timaeus:
“If intelligence and true belief are two different kinds, then these things – Forms that we cannot perceive but only think of – certainly exist in themselves… There is, first, the unchanging Form, ungenerated and indestructible, which neither receives anything else into itself from elsewhere nor itself enters into anything anywhere, invisible and otherwise imperceptible; that, in fact, thinking has for its object…Second is that which bears the same name and is like that Form; is sensible; is brought into existence, is perpetually in motion, coming to be in a certain place and vanishing out of it; and is to be apprehended by belief including perception…Third is space which is everlasting, not admitting destruction; producing a situation for all things that come into being, but itself apprehended without the senses by a sort of bastard reasoning, and hardly an object of belief.”4
We are left perhaps befuddled by Plato’s theory. Does Plato actually believe that our mental understanding of the properties of reality is more real than the world from which we abstract those ideas? Plato himself challenges the theory of the Forms in later dialogues (for example, Parmenides). His most famous student, Aristotle, certainly rejected this ethereal view of reality. However, in modified form, Plato’s theory survived into Neoplatonism and Christianity, and reverberates to some extent in Berkley, Kant, and Schopenhauer among others. Bertrand Russell however thinks Plato is conflating the Forms with the ‘universals.’5
For myself, I think Plato is at least partly correct to assign ultimate reality to the Forms. At the level of some concepts – for example mathematical ones – existence seems to be independent of the human mind. Just as we assume that the universe was real prior to our existence even though we were not here to witness it; similarly, it is reasonable to assume should humans become extinct, other rational beings will be able to recognize the concept of a perfect circle or the number 2. Plato seems to be the first philosopher to endorse a more expansive view of nonphysical reality – the principle that not just ‘Thought” but specific ‘thoughts’ or Ideas have ‘being.’ In a different sense, Plato’s Forms represent the never quite reachable limits of perceptual reality, such as we understand in a differential equation or the notion of infinity.
In conclusion, it seems to me we owe to Plato two novel nuances of the meaning of ultimate reality: the somewhat abstract concept of the divine as the Supreme Good, and the output of the mind as fundamentally real, if not more real, than the material constituents of the world.
4Allen, Reginald E., Greek Philosophy: Thales to Aristotle. The Free Press, New York, NY, 1966. Page 252-253.