George Eliot speaks to Aristotle about metaphor
From The Mill on the Floss
"But Mr. Stelling took no note of these things; he only observed that Tom's faculties failed him before the abstractions hideously symbolized to him in the pages of the Eton Grammar, and that he was in a state bordering on idiocy with regard to the demonstration that two given triangles must be equal, though he could discern with great promptitude and certainty the fact that they were equal. Whence Mr. Stelling concluded that Tom's brain, being peculiarly impervious to etymology and demonstrations, was peculiarly in need of being ploughed and harrowed by these patent implements; it was his favorite metaphor, that the classics and geometry constituted that culture of the mind which prepared it for the reception of any subsequent crop.
"I say nothing against Mr. Stelling's theory; if we are to have one regimen for all minds, his seems to me as good as any other. I only know it turned out as uncomfortably for Tom Tulliver as if he had been plied with cheese in order to remedy a gastric weakness which prevented him from digesting it.
"It is astonishing what a different result one gets by changing the metaphor! Once call the brain an intellectual stomach, and one's ingenious conception of the classics and geometry as ploughs and harrows seems to settle nothing. But then it is open to someone else to follow great authorities, and call the mind a sheet of white paper or a mirror, in which case one's knowledge of the digestive process becomes quite irrelevant.
"It was doubtless an ingenious idea to call the camel the ship of the desert, but it would hardly lead one far in training that useful beast. O Aristotle! if you had had the advantage of being "the freshest modern" instead of the greatest ancient, would you not have mingled your praise of metaphorical speech, as a sign of high intelligence, with a lamentation that intelligence so rarely shows itself in speech without metaphor,-that we can so seldom declare what a thing is, except by saying it is something else?"
What more could one say to Aristotle after Eliot's address in the last paragraph.
Steven Pinker on metaphor
Steven Pinker, a linguist with a fundamental evolutionary perspective, has written five popular works on the mind and its relation to language: The Language Instinct (1994), How the Mind Works (1997), Words and Rules (1999), The Blank Slate (2002), and The Stuff of Thought (200x). The following excerpts an interview with Marion Long, published in Discover Magazine:
....I have two superheroes....One of them is metaphor, the other combinatorics. Metaphor would be the way in which we transfer and transform ways of thinking that came from the realm of very concrete actions like pouring water or throwing rocks or closing a jammed drawer, and so on. But we can leach the content from them and use them as abstract structures to reason about other domains. We can talk about the economy rising and falling, as if it were a domain....
An enormous amount of scientific language is metaphorical. We talk about a genetic code, where code originally meant a cipher; we talk about the solar system model of the atom as though the atom were like a sun and moon and planets. And although we use these metaphors of concrete things to stand for abstract concepts, that doesn’t keep us from putting a different twist on those same metaphors of the concrete and using them to describe other and quite different abstract concepts. When we put together the power of metaphor with the combinatorial nature of language and thought, we become able to create a virtually infinite number of ideas, even though we are equipped with a finite inventory of concepts and relations. I believe it is the mechanism that the mind uses to understand otherwise inaccessible abstract concepts. It may be how the mind evolved the ability to reason about abstract concepts such as chess or politics, which are not really concrete or physical and have no obvious relevance to reproduction and physical survival....
We must tap the mind’s ability to grasp things in familiar ways and then to stretch them to apply to new ideas and areas of thought. But we also have to be mindful of the fact that there are ways in which any metaphor may or may not correspond accurately to the thing you’re using it to explain….To make it true and useful, one then has to add all these qualifications, like, well, yes, it’s like this in one regard but not in another. So, for example, the mind is like a computer in that it depends on information storage, but it’s not like a computer in that its accuracy isn’t highly reliable and it doesn’t work serially but rather in parallel. Or that natural selection is like a design engineer in the sense that parts of animals become engineered to accomplish certain things, but it is not like a design engineer in that it doesn’t have long-term foresight. 
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- Marion Long (2007) Discover Interview Why Has Steven Pinker Studied Verbs for 20 Years? Interview. Discover Magazine. September 2007 issue.