A closeup of Plato in Raphael's 1509–1511 fresco, The School of Athens.
Plato, born in the 5th century BCE, helped birth Western philosophy. His ideas, to this day, continue to be greatly influential.
Speaking of which, Plato came up with ‘universal Ideas’: what we will call ‘Forms’ here.
Plato believed that there was a reality which was unchanging, eternal and outside of perception: a ‘Platonic reality’, we now say. Connected to every object or idea, he said, outside of space and time, is an eternal form—its Form.
Forms are basically ideal versions of things. For example, there is a Form of the good, of marriage, of colours, of beauty, of dogs, of bananas, and so on. They exist in the realm of Forms, abstractly or really, depending on what kind of Platonism we subscribe to. Forms have essences and are the purest of all things: a blueprint, guiding us. They can make the world better; we just have to engage them philosophically.
In fact, the realm of Forms is the most-fundamental reality there is: it sits before logic, geometry, mathematics, natural sciences, and other areas inside our visible and intelligible domain—‘itself by itself with itself’ (Plato, The Symposium). The world we inhabit, which is revealed by our senses, is not real but an imperfect copy—a material imitation.
This schema was put into metaphorical form by Plato in the ‘Allegory of the Cave’, which, in turn, has inspired films such as The Truman Show (1998) and The Matrix (1999). Shadows cast in the cave; a life on reality TV; a life inside a simulation—similarly, on Earth we see particular objects and ideas which mimic Forms.
What Plato attempted to do was solve the problem of universals: that is, try to figure out how properties exist with respect to the objects and ideas they belong to. His answer: they are derived from Forms, giving us ambitions to strive towards in our humanly conceptions.
But was his idealism realistic enough?