A really important work for me is the essay "What is Literature?" by the French existentialist philosopher Jean-Paul Sartre. I've embedded the essay here—I think it's definitely worth a read if you've got the time. The first few pages, though, are where Sartre deals most explicitly with how art—painting, music, poetry, prose, etc.—functions representationally. On page 30, in a turn that doesn't seem too out of line with Plato's thoughts about poetry in The Republic, Sartre notes that
For the poet, language is a structure of the external world. The speaker isin a situation in language; he is invested by words. They are prolongations of his senses, his pincers, his antennae, his spectacles. He manœveres them from within; he feels them as if they were his body; he is surrounded by a verbal body which he is hardly conscious of and which extends his action upon the world. The poet is outside language. He sees the reverse side of words, as if he did not share the human condition and as if he were first meeting the word as a barrier as he comes towards men. Instead of first knowing things by their name, it seems that first he has a silent contact with them, since, turning towards that other species of thing which for him is the word, touching words, testing them, fingering them, he discovers in them a slight luminosity of their own and particular affinities with the earth, the sky, the water, and all created things.
Not knowing how to use them as a sign of an aspect of the world, he sees in the word the image of one of these aspects. And the verbal image he chooses for its resemblance to the willow tree or the ash tree is not necessarily the word which we use to designate these objects. As he is already on the outside, he considers words as a trap to catch a fleeing reality rather than as indicators which throw him out of himself into the midst of things. In short, all language is for him the mirror of the world. As a result, important changes take place in the internal economy of the word. Its sonority, its length, its masculine or feminine endings, its visual aspect, compose for him a face of flesh which represents rather than expresses meaning. Inversely, as the meaning is realized, the physical aspect of the word is reflected within it, and it, in its turn, functions as an image of the verbal body. Like its sign, too, for it has lost its preeminence; since words, like things, are given, the poet does not decide wheter the former exist for the latter or vice versa.
What Sartre's getting at here, I think, is that poets don't occupy the same sort of philosophical space as prose writers because their approach to language is based in creation. "Suppose the painter portrays houses?" Sartre asks on page 27. "That's just it. He makes them, that is, he creates an imaginary house on the canvas and not a sign of a house." This is the function of the poet as well, to create an image rather than a representation of one.
I don't mean for this to be my presentation, but it's something that I've been exploring and I thought some other folks might find it interesting as well. The rest of the essay diverges from a discussion of art, less out of Sartre's dismissal of poetry than his primary interest in what literature means as a method of communication and an expression of human freedom. Let me know what you think.