The rules that govern metaphors and allegories, are of two kinds: those of the first kind concern the construction of a metaphor or allegory, and ascertain what are perfect and what are faulty: those of the other kind concern the propriety or impropriety of introduction, in what circumstances these figures may be admitted, and in what circumstances they are out of place. I begin with rules of the first kind; some of which coincide with those already given with respect to similes; some are peculiar to metaphors and allegories.
And in the first place, it has been observed, that a simile cannot be agreeable where the resemblance is either too strong or too faint. This holds equally in a metaphor and allegory; and the reason is the same in all. In the following instances, the resemblance is too faint to be agreeable.
Malcolm.—— But there’s no bottom, none,
In my voluptuousness: your wives, your daughters,
Your matrons, and your maids, could not fill up
The cistern of my lust.
Macbeth, act 4. sc. 4.
The best way to judge of this metaphor, is to convert it into a simile; which would be bad, because there is scarce any resemblance betwixt lust and a cistern, or betwixt enormous lust and a large cistern.
Again,
He cannot buckle his distemper’d cause
Within the belt of rule.
Macbeth, act 5. sc. 2.
There is no resemblance betwixt a distempered cause and any body that can be confined within a belt.
Again,
Steep me in poverty to the very lips.
Othello, act 4. sc. 9.
Poverty here must be conceived a fluid, which it resembles not in any manner.