Nelson Goodman "Languages of art", page 79-80. http://books.google.com/books?id=e4a5-I ... &q&f=false
"Truth of metaphor does not, indeed, guarantee its effectiveness. As there are irrelevant, tepid and trivial literal truths, there are farfetched, feeble and moribound metaphors. Metaphorical force requires a combination of novelty with fitness, of the odd with the obvious. The good metaphor satisfies while it startles. Metaphor is most potent when the transferred schema effects a new and notable organization rather than a mere relabeling of an old one. Where the organization by an immigrant schema coincides with an organization already otherwise effected in the new realm, the sole interest of the metaphor lies in how this organization is thus related to the application of the schema in its home realm, and sometimes to what the labels of the schema exemplify. But where an unaccustomed organization results, new associations and discriminations are also made within the realm of transfer; and the metaphor is the more telling as these are the more intriguing and significant. Since metaphor depends upon such transient factors as novelty and interest, its mortality is understandable. With repetition, a transferred application of a schema becomes routine, and no longer requires or makes any allusion to its base application. What was novel becomes commonplace, its past is forgotten, and metaphor fades to mere truth."