What, then, is Plato’s answer to this colossal challenge set by Glaucon? How is he to show we should remain just people even when being burnt at the stake for allegedly committing theft and murder?
He starts his answer by returning to The Republic‘s initial question: what is justice? And this is because he doesn’t think we can truly know whether something is beneficial until we have first established what that thing is. So in defining justice, he rejects theories which talk about ‘giving each man his due’, for instance, and instead focuses on the idea that justice is a kind of mental harmony. So I am just if I have the right psychic balance. And, inevitably, he must think that this explanation of justice can explain why we say that stealing, murdering and so on are examples of it.
To explain what the psychic balance involves, he must first identify the mind’s parts. So Plato suggests we think of the mind as being made up of three bits: our appetite, which is instinctive and seeks various pleasures; our spirit, which gets angry out of a sense of shame; and our reason, which searches for knowledge and cares for the wellbeing of the individual as a whole. So by its very nature, reason is designed to be in control. It must keep a check on the appetites and ensure they don’t run wild, and the spirit, it seems, must grow to align with reason and execute its demands. And when this state is reached, the person will be just, and just actions will follow accordingly.
Why does Plato think mental harmony suffices for ensuring one refrains from stealing? Because he assumes the only motives one could have for stealing stem out of desires based on pleonexia: the Greek word for greed. And this, by definition, flows from appetites which are getting an excessive say and thereby ensuring you act unjustly. If reason were in control, it would safeguard against such action.
How does this show, exactly, that justice is always beneficial? Well, the answer becomes obvious. If justice is a form of mental health, then injustice is an illness, and so it makes no sense to say injustice is ever beneficial. It may mean that you get more ‘goods’ like money, sex or whatever, but if that requires a mental state in which your appetite is out of control and violates its proper function, then intentionally pursuing injustice and saying it’s valuable is like a builder praising his construction of a leaky house. Houses, and actions, have evaluative criteria built into them, and the criterion for a good act is necessarily that it does not contribute to a corrupted mind. So when you’re burnt at the stake by Glaucon’s imaginary people because you’re mistaken for a criminal, it may hurt and your death may be terrible. But it would never be worse than the alternative, which would allow you to stay alive, but only physically. By practising injustice, your mind would have been destroyed long ago.
Picture: a horse and chariot. This is one way of understanding Plato’s picture of the soul in which reason rules over one’s appetites. The unjust man would have his horses running wild, and the man in the cart being trampled upon.