3. Metaphors should avoid mean or disagreeable details.
4. Metaphors should not be forced. Some metaphors are so far-fetched that (as Mr. Lowell says) one could wish their authors no worse fate than to be obliged to carry them back whence they came.
5. Do not mix literal and metaphorical language. In the sentence
I was walking on the barren hills of sin and sorrow near Welshpool,
“the barren hills of sin and sorrow” is metaphorical, and “near Welshpool” is literal.
Examples of Apt Illustrations.
But I am constant as the northern star,
Of whose true-fix’d and resting quality
There is no fellow in the firmament.—Shakespeare.
I had rather be a dog and bay the moon,