Aristotle, Rhetoric
J. H. Freese, Ed.

[13] Metaphors should also be derived from things that are beautiful, the beauty of a word consisting, as Licymnius says, in its sound or sense, and its ugliness in the same. There is a third condition, which refutes the sophistical argument; for it is not the case, as Bryson¹ said, that no one ever uses foul language, if the meaning is the same whether this or that word is used; this is false; for one word is more proper than another, more of a likeness, and better suited to putting the matter before the eyes. Further, this word or that does not signify a thing under the same conditions; thus for this reason also it must be admitted that one word is fairer or fouler than the other. Both, indeed, signify what is fair or foul, but not qua fair or foul; or if they do, it is in a greater or less degree. Metaphors therefore should be derived from what is beautiful either in sound, or in signification, or to sight, or to some other sense. For it does make a difference, for instance, whether one says “rosy-fingered morn,” rather than “purple-fingered,”
or, what is still worse, “red-fingered.”