"For not by art does the poet sing, but by power divine. Had he learned by rules of art, he would have known how to speak not of one theme only, but of all; and therefore God takes away the minds of poets, and uses them as his ministers, as he also uses diviners and holy prophets, in order that we who hear them may know them to be speaking not of themselves who utter these priceless words in a state of unconsciousness, but that God himself is the speaker, and that through them he is conversing with us."

Source: Plato (2002). “Plato: Five Dialogues: Euthyphro, Apology, Crito, Meno, Phaedo”, p.27, Hackett Publishing