“. . .there are many other things I have found myself saying about poetry, but the chiefest of these is that it is metaphor, saying one thing and meaning another, saying one thing in terms of another, the pleasure of ulteriority. Poetry is simply made of metaphor. So also is philosophy–and science, too, for that matter, if it will take the soft impeachment from a friend. Every poem is a new metaphor inside or it is nothing. And there is a sense in which all poems are the same old metaphor always.”
From “The Constant Symbol”, an essay by Robert Frost in Atlantic Monthly, October 1946.