I bridle in my struggling Muse with Pain That longs to launch into a nobler strain.
To bridle a goddess is no very delicate idea; but why must she be bridled? because she longs to launch, an act which was never hindered by a bridle : and whither will she launch? Into a nobler strain. She is in the first line a horse, in the second a boat, and the care of the poet is to keep his horse or his boat from singing.
Samuel Johnson, Life of Addison1
There is a sense in which the examples cited so far do not offer any linguistic difficulties; and one in which metaphors seem to do so. The difference is often supposed to lie in a distinction between the literal and the figurative uses of language. Thus if we compare
John put on his friendliest and most sincere expression and walked toward the man
the sweet small clumsy feet of April came into the ragged meadow of my soul2
we feel that the former has a direct and explicable relationship to its situation or possible state of affairs, whereas the latter has not. And yet both make assertions.3 The grounds of this contrast are very difficult to specify in the present state of our knowledge,4 even though mature speakers do seem to 'be able to say with certainty which are metaphorical uses of language.5 We may then be able to make the initial hypothesis that we internalize 'normal' uses of language and can recognize figurative language as a 'deviant' use which is in some way foregrounded against these literal norms.6
I follow Max Black in using the terminology of 'focus' for the deviating component, and 'frame' for the literal language which surrounds it.7 Thus for the examples
The chairman ploughed through the discussion
The ship ploughs the sea
'ploughed' and 'ploughs' are the foci, and yet there could be literal ways of filling in the frame (with 'slept', 'took notes', 'sails', and so on). This mode of analysis has of course no great rigour. It can only be used to suggest part of the psychological process by which we may recognize that we have a metaphor'to deal with.