Poetry and prose, however different in language, overlapped, almost coincided, in content. But modern poetry, if it ‘says’ anything at all, if it aspires to ‘mean’ as well as to ‘be,’ says what prose could not say in any fashion. To read the old poetry involved learning a slightly different language; to read the new involves the unmaking of your mind, the abandonment of all the logical and narrative connections which you use in reading prose or in conversation. You must achieve a trance-like condition in which images, associations, and sounds operate without these. Thus the common ground between poetry and any other use of words is reduced almost to zero. In that way poetry is now more quintessentially poetical than ever before; ‘purer’ in the negative sense. It not only does (like all good poetry) what prose can’t do: it deliberately refrains from doing anything that prose can do.
—C. S. Lewis, from “Poetry,” in An Experiment in Criticism (Cambridge University Press, 1961)