Metaphor, Analogy, Abstraction, Method

'Strictly speaking, metaphor occurs as often as we take a word out of its original sphere and apply it to new circumstances.  In this sense almost all words can be shown to be metaphorical when they do not bear a physical meaning; for the original meaning of almost all words can be traced back to something physical; in our first sentence above, for instance, there are eight different metaphors. Words had to be found to express mental perceptions, abstract ideas, and complex relations, for which a primitive vocabulary did not provide; and the obvious course was to convey the new idea by means of the nearest physical parallel.'  (Henry Fowler, The King's English)

I like this quote because it indicates a deep relationship between metaphor and abstraction -- the act of abstraction is the first step in the metaphor, and the second step is the application of the abstracted method to the new domain.  The graft takes if the two contexts are analogous; that is, if the relevant meanings inherent in them are commensurable though different.  Analogy is defined by equivalence of methods: 'what works here, also works there'.

But equivalence is not indistinguishability, and the difference between domains is what gives force to the metaphor: the power of a metaphor is proportional to how much variety it can successfully subsume under a common method.  When we lose sight of the differences, the metaphor becomes 'dead', i.e. nolonger capable of evoking the same emotion.  When the differences suddenly reassert themselves in the form of a contradiction, the magnitude of the emotion felt is apt to be proportional to that of the living metaphor -- albeit with the sign reversed!