Metaphor and how it works

Here was a quick "parts of metaphor and how it works" handout that I gave my class this week:

If figurative language is (speaking broadly) language that says what it says only by meaning more than what it says, then metaphor is language that means more by comparison or the assertion of identity between one thing and another (not just likeness, which is a simile). Put more exactly, a metaphor is language that gives you two elements. These are the tenor and vehicle (for a more in depth discussion of this, see my post on tenor and vehicle as discussed by I.A. Richards):

The tenor is what is to be compared or is said to be identical, which will be the underlying “drift” or idea or attitude that is conveyed.

The vehicle is the thing to which something has been compared or has been said to be identical, which will be the thing through which the idea is conveyed.

Let's look at these elements and how they make up the metaphor in a passage from Locke:

When their Children are grown up, and these ill Habits with them; when they are now too big to be dandled, and their Parents can no longer make Use of them as Play-things, then they complain that the Brats are perverse; then they are offended to see them willful, and are troubled with those ill Humors which they themselves infused and fomented in them; and then, perhaps too late, would be glad to get out those Weeds which their own Hands have planted, and which now have taken too deep Root to be easily extirpated.
-John Locke, Some Thoughts Concerning Education (§35, 21-22).

In the “Weed” metaphor in the last part of the sentence, the tenor is ill habits and the vehicle is weeds. The vehicle conveys or carries the tenor; or, to speak less metaphorically (and more awkwardly), the weeds, to which the idea of ill habits has been compared, are what convey the idea. The vehicle, if extended, conveys the tenor by continually qualifying it. So as Locke’s weed-metaphor keeps developing with the addition of “planted” “taken […] Root” and “extirpated,” we have to make the tenor more specific: the ill habits aren't just any ill habits, but ones that spread in the child and seem to resist any attempt to pull them out of him. At the same time, this reacts back upon the vehicle: the weeds we are talking about were at some point actually weed-seeds that had to be planted, etc.

Remember though that the metaphor is our name for what gives you both tenor and vehicle: not the latter only and certainly not the former only. That is, metaphor is the comparison as a whole, and thus if the vehicle cannot be distinguished from the tenor, the part of the statement under consideration is literal, because there is no comparison going on. Even with this limit, though, most sentences in fluid discourse turn out to be metaphoric, or surprisingly few turn out to be purely literal (in the passage from Locke, even excepting the last part of the sentence, we have “Play-things,” “infused,” and “fomented,” as well as “grown up,” “big,” and perhaps even “make” and “troubled” if they are not too dead).

We can also speak of the ground of the metaphor, which is the actual commonality between the tenor and vehicle: thus the vehicle conveys the tenor over the ground (to extend our metaphor). The ground can only sometimes be found—unlike with a simile, where it can always be found. In extended metaphors, the ground will become broader as more vehicles carry the tenor; or, to put it another way, the vehicle will begin to qualify the tenor. For the whole extended metaphor, the ground is the commonality between a child a plant (“growing up,” with which the passage starts, is key here, and probably led Locke to use this metaphor). A catachresis or mis-applied metaphor, however, is one where the ground becomes obvious because it would have to be inappropriate or absurd (the classic example is the “leg” of a table, though this is not as absurd as some), and usually occurs when a vehicle conflicts with another vehicle (in what we colloquially and metaphorically call “mixed” metaphor, e.g. Hamlet’s “Take arms against a sea of troubles”).