In Book III of the Republic, Plato considered art. He claimed that there were two kinds of art:
1) Representational - the aritst puts himself in the role(s) of the participants
2) Narrative - the artist observes and reports the actions of the participants through indirect speech, scenes, etc.
Plato objected to representational art, involving mimesis:
a) each should fulfill his own role and not take on others' (397e); this is an echo from his tripartite soul and the idea of justice relating to the correct functioning of this soul
b) putting oneself in the role of a bad person will corrupt you (396c-d)
Representational art is only acceptable when the artist assumes the role of a good person that is similar to his own, such that it promotes virtue
By the end of Book III Plato more or less comes to this conclusion, and bans all representational art that does not imitate good people.
But Plato then changes his mind slightly in Book X, setting up a distinction between the artist and the craftsman:
1) In making things, craftsmen are guided by forms, and instantiate these forms in physical objects, representing these forms as best they can. This form of mimesis is unobjectionable, even laudable, according to Plato.
2) Artists, however, are guided by the physical instantiations of forms, and so are imitating imitations, and thus "the artist's representation stands at third remove from reality" (597e), in that it is an instantiation of an imitation of an imitation.
Plato said that in drawing the soul to consider third removes from forms rather than the forms themselves, artists appeal to the lower parts of the soul, and distract men from the higher virtues of philosophy. Art cannot appeal to reason since the rational person will know how removed from the forms art actually is.
Plato therefore advocates banning all representational art, and claims he came to the selfsame conclusion in Book III. Given its greater coherence with his other claims about the soul and the forms, Book X should be taken to be his more considered opinion, and a refinement of Book III's conclusions.
Objection: Tate, Cross and Woozley distinguish between two senses of imitation:
1) Good imitation - where the artist imitates with the knowledge that the subject is good
2) Bad imitation - where the artist imitates without knowledge or without regard to knowledge of the subject, and so imitates mere appearances
In this sense, they claim, the good kind of imitation ought to be OK since the guardians will be imitating their own ideal character, and so drawing attention to it. But that claim is still open to the problem of its remove from the forms, and Plato might argue in return that though 'good imitation' might be better than 'bad imitation', it still removes the mind further from the forms than philosophy and crafstmanship, and so guardians should take the opportunity to ban art for the sake of the people, that they might concentrate on the higher pursuits.
Objection: some art may merely be a representation of an imitation of an instantiation of a form, but one can distinguish between that base art and higher forms of art, which go beyond crastsmanship to try to represent or communicate ideas based upon the forms. Abstract painting, for example, looks beyond mere appearances and asks us to appreciate the forms behind that instantiation. And a good novel can use third-removed imitation in the form of imaginary characters to explore the highest forms of the good, the beautiful, etc., something that crasfmanship cannot achieve.
Plato's mistake here might in part be based upon the kind and quality of art in his time, and perhaps also on his ability to comprehend and appreciate it. Had he enjoyed a full appreciation of all art from his time until the present day, he might have come to a different conclusion. Then again, one could argue that the art world reacted to Plato's criticisms and looked to the forms for inspiration; this seems unlikely, given the roots of the more expressive artists of our time and from times past, but certainly Plato's legacy of the forms combined with popular religions must have been formative in this movement away from mere imitation.