In the tenth book of the Republic, when Plato has completed his final burning denunciation of Poetry, the false Siren, the imitator of things which themselves are shadows, the ally of all that is low and weak in the soul against that which is high and strong, who makes us feed the things we ought to starve and serve the things we ought to rule, he ends with a touch of compunction: 'We will give her champions, not poets themselves but poet-lovers, an opportunity to make her defence in plain prose and show that she is not only sweet--as we well know--but also helpful to society and the life of man, and we will listen in a kindly spirit. For we shall be gainers, I take it, if this can be proved.' Aristotle certainly knew the passage, and it looks as if his treatise on poetry was an answer to Plato's challenge.