Simon Critchley writes:

In the Republic, Socrates and Plato’s brothers wander out of Athens and walk down to the port of Piraeus, leaving the city behind them. After quickly demolishing the prevailing views of justice in Athenian society, Socrates proceeds to dream of another city, a just city governed by philosophers whose souls would be oriented towards the Good. The familiar objection to Plato, that the ideal of the philosophical city is utopian or impossible to realise, is fatuous. Of course the philosophers’ city is utopian: that is the point. You might argue that it is the duty of philosophy to think in a way that allows us to believe another world is possible, however difficult it would be to achieve.

(LRB 20 September 2007)