Plato never dealt with aesthetics as such, since art theory never figured among its investigations; but in La República and La Leyes he did refer many times to the problems of art and beauty. Aesthetic questions are intertwined in their thinking with metaphysical and ethical, which influence the former. In their texts, for the first time, beauty and art were included in a great philosophical, idealistic, spiritualist and moralistic system.
For Plato the proof of the existence of beauty is an innate sense of the beautiful, and not an ephemeral feeling of pleasure. To understand us: not everything we like is beautiful really, sometimes it just appears. There is a true beauty opposed to an illusory beauty.
The capture of the beautiful is for Plato a particularity of man that manifests our kinship with the gods.
Assuming (although enlarging) the Pythagorean conception of beauty as order, proportion and harmony, he censured the Athenian art of his time, considering that he had lost the measure and distinguished between good art (the one based precisely on the measure) and bad art. (the one supported by the sensory and emotional reactions of men), because he did not consider the beautiful forms superior to the content.
