Plato was Socrates's most famous protégé. He continued the Socratic legacy while building on it with his own theories. He also founded a school of philosophy, rather generically called The Academy. The basis of his mission and his goals can be found in his allegory of The Cave.
This story is meant to illustrate how the majority of people live with a veil over their eyes, with only a distorted and shadowy notion of such things as Truth and Beauty. Imagine a group of shackled individuals in a dimly lit cave illuminated only by a large fire behind them. These cave people can only see shadows of themselves and other images flickering on a wall before them. This is their reality.
Most are either unimaginative or apathetic and simply accept this reality without speculation. The more inquiring minds observe the patterns more clearly and try to understand their world. Yet Truth eludes them.
One of the prisoners manages to break free from his shackles and escape the cave. Emerging into the light of day, this escapee is blinded by the light, again only seeing a shadowy representation of reality. Over time, however, this person will acclimate his senses to his surroundings and see things more clearly: the landscape, the sky, and the sun's illumination.
Eventually, this newly enlightened soul returns to the cave and tries to spread word of the brave new world that exists beyond the claustrophobic confines of the cave. What will the response of the cave dwellers be? Will they boldly go where this citizen had gone before and take the arduous yet rewarding journey out of darkness and into the light? No, according to Plato. They are more likely to kill the prophet, because he is a threat to the status quo.
This is an obvious reference to Plato's mentor Socrates, and a commentary on humanity's predilection to choose the fogbound existence, the easier and the softer way, the don't-rock-the-boat mentality. And the philosophers that lead the way are usually denounced, derided, and often end up dead.
In his eighty years (a very long life in those days), Plato established himself as the philosopher all other philosophers look to for inspiration. Some concurred with, adapted, and expanded upon his theories, others disputed and countered them, but all were influenced by him.
Plato was a firm believer in Ideas with a capital I or, as they are also called, Forms. Plato believed that while we can admire the beauty of a windswept beach, or the buff bods on said beach, there exists, out there in the ether, the Form of Beauty. The Idea of Beauty was an entity that imbues all the beauty we see in physical reality. The cast of
Knowledge is fourfold, according to Plato.
The knowledge from imagination, dreams, and what was later called the unconscious
Our perceptions of the outside world
Philosophical knowledge, which was Big Picture knowledge, an awareness of absolutes, universal truths in the form of those elusive Forms
Plato called the first two mere opinions, because while perception may be reality, things are perceived differently by different people. The second two were True Knowledge, because Plato believed that two plus two will never equal five, and Forms are immutable, eternal truths not to be messed with.
Where does God fit in this picture, you may ask? Plato believed that there was one Form among the Forms called the Good, and this has been interpreted as God. This mysterious realm where the Forms dwell is the true reality, according to Plato, and we poor creatures merely loom in the shadowy cave of our reality.
Plato, like Pythagoras before him, also believed in reincarnation. We have all lived before and will live again. And in the meantime, in between time, in the period after death and before rebirth, we have access to the realm of the Forms and we can finally “get it.” Aye, but there's a rub, as there always is. Once we return to the earthbound realm, we forget about all we can comprehend in the heavenly realm, only retaining a dim and nagging awareness that there is something greater than ourselves out there. And this never-ending quest to reclaim that lost knowledge is what makes potential philosophers of us all. For those seeking a little hellfire and brimstone in their theology, it is worth noting that Plato believed that the truly evil among us do not have the option to return in another life.
They are condemned forever. The world of the senses, and of sensual pleasure, actually inhibits finding true happiness, because it makes us more grounded in the real world, which is, according to Plato, not the highest reality.