"How should one live" according to Plato, Socrates, and Aristotle.

Plato is famed for his quip "The unexamined life is not
worth living". (Actually, Socrates is given credit for this, but it is difficult to
separate Plato from Socrates. So for our purposes we will keep them as one and the
same). But what Plato meant is not what the modern person might think this statement
means. To the modern mind, this statement means to be introspective and think of what
life may mean to you, in a relativistic sense. But for Plato, it did not mean this
exactly.

Plato was a Rationalist, which means Reason
(capital R) is what is the most important thing. It ultimately is what allows us to be
happy.

Plato's Allegory of the Cave is his best effort to
explain how we should live. Imagine a cave. Now imagine prisoners chained in such a way
that they can only see one wall in front of them and they are not able to move their
heads.  Above and behind them is a fire which case shadows onto the wall the prisoners
see. This is all they have ever seen and do not understand that it is people and objects
that are making the shadows. The prisoners think that shadows are
reality.

Now imagine that one prisoner is unchained and is
turned around and forced to look at the real things that cause the shadows. His eyes
hurt and he complains that he wants to only see shadows. Next, the prisoner is forced up
out up the cave and into the sun, into the real world. THe sun blinds him at first. Bur
gradually, over time, he is able to see the sun itself.

The
jouney of this prisoner is an allegory for our own journey to see and understand the
Truth (capital T). According to Plato there are four levels of knowledge: Conjecture,
(images like shadows or TV), Belief (based on objects or particular things),
Understanding (represented by the prisoner who realizes that shadows are caused by
objects) and finally, Pure Reason (knowledge of the Forms, or things in
themselves).

According to Plato, we should live our life
trying to understand the eternal Truths (Plato's Forms). When we understand the Form of
something, we are like the prisoner being freed from the cave. At first it hurts, but
gradually we come to see Truth. On Plato's view, humans cannnot be happy unless they are
able to understand the Forms.

OK..that is a rather
simplified view of Plato, but hopefully it answers your question about him. Aristotle
will be a separate answer.