The Republic by Plato Part 10 Page 13

And so, when we hear persons saying that the tragedians, and Homer, who is at their head, know all the arts and all things human, virtue as well as vice, and divine things too, for that the good poet cannot compose well unless he knows his subject, and that he who has not this knowledge can never be a poet, we ought to consider whether here also there may not be a similar illusion. Perhaps they may have come across imitators and been deceived by them; they may not have remembered when they saw their works that these were but imitations thrice removed from the truth, and could easily be made without any knowledge of the truth, because they are appearances only and not realities? Or, after all, they may be in the right, and poets do really know the things about which they seem to the many to speak so well?

The question, he said, should by all means be considered.