A metaphor is a literary device, a comparison between two dissimilar things, using descriptive or figurative language, for rhetorical effect. Metaphors are a great way to add colour to your descriptions and spice up your writing.
By using symbolism, they tell us more about the subject than a literal description. They create a shortcut to understanding, ‘a way of holding the most meaning in the least space’. Aristotle said a metaphor was ‘the act of giving a thing a name that belongs to something else’. By doing that, we can say so much more about something than if we were to convey that meaning in a long, boring, literal paragraph.
A metaphor comprises a tenor—the subject of the metaphor—and a vehicle—the thing that illustrates the metaphor. In ‘the falling snow glittered like a shower of tiny silver coins’, for example, the snow is the tenor and the coin-shower is the vehicle. I would add that there is also an element of purport. In that example, there is extra meaning implied. We feel that there is something valuable, like coins, about the snow.
I include under this banner simile—saying the tenor is like the vehicle—and synecdoche—using a part of something to represent the whole. The above phrase about the falling snow is a simile—the snow is like the coin-shower; a metaphor would be ‘a shower of silver coins fell all around me, and I hugged my coat tightly against the cold’—the coin-shower is used to represent the falling snow, which is not expressed. ‘All hands on deck’ is a synecdoche—the partial hands represents the entire bodies of the whole crew. One might also include allegory, which is a longer, sustained comparison that makes up a whole story.
So, what makes a wonderful metaphor?
Never seen before
A wonderful metaphor should, first and foremost, not be a cliché. George Orwell said, ‘Never use a metaphor, simile or other figure of speech which you are used to seeing in print.’ You’re not going to set your reader’s heart thumping by describing the shack in the woods that’s ‘as old as the hills’ or having your protagonist surprised by something ‘like a bolt from the blue’. Also avoid using too many metaphors, especially if they seem more for the purpose of sounding gorgeous than for conveying purport. This is called ‘purple prose’.
You may find multiple lists of clichés on the Internet, and there is even software that will purge your copy of them ProWritingAid’s (free) Cliché Check. So, avoiding clichés is the easy part. What to write, instead?
Use gorgeous words
To begin with, choose gorgeous words. There are tricks you can use to dress up your phrases—repetition, alliteration, using rhyming words. Cadence is something you could play around with.
We’re used to limericks being dadadadadadadada, dadadadadadadada, dadadadadi, dadadadadi, dadadadadadadada. When we hear that meter and rhyming scheme, before we even get to the punchline, we’re expecting it to be funny. Ancient Greek and Roman poetry used specific meters for each type of poem. For example, eulogies were written in couplets, one verse hexameter, one pentameter. When ancient Romans heard that meter, before even comprehending the words of the poem, they felt sad.
Read your phrase out loud. How does it rise and fall? Is it short and sharp, quickening your story’s Pace, or long and languid, slowing things down? How do you want the reader to feel?
Be time and place specific
You should never use words or phrases that would be anachronistic to your character. You can’t have your 16th century hero keeping secrets ‘on the down low’. The corollary to that is that you should always use metaphors in keeping with your story’s genius loci (the spirit of the place).
Be voice specific
Your metaphors should tally with the Voice of your Point of View character. If she’s a pianist, you could lean heavily to musical metaphors; if he’s a preacher you could use biblical references. If he’s an old man, you could use rather old-fashioned words. Olde-worlde peasants would probably use a lot of agricultural metaphors. A surprised person would ‘open and close his mouth like a dying fish’, which conveys the additional meaning that the person felt hurt by the surprise.
Think of characterisation
Metaphors can tell you something about the person they are describing; they can also tell you about the person who’s doing the describing. In Rebecca Horsfall’s Dancing on Thorns, the protagonist describes a man she’s just started dating. ‘When he laughs [his face] crinkles up like an apple that’s been left in the fruit bowl for a month.’ We infer that the man in no looker, but he’s a jolly sort. We also learn that she likes men who laugh. In context we know that she’s comparing him to her ex, so we learn that her ex was not much of a laugher and perhaps that she didn’t like that about him.
Stimulate the senses
What does your reader see, smell, hear, feel? What are the defining characteristics of your tenor; think of them using your senses. What have you seen, smelled, heard, felt about that thing, scene, situation, person? What objects, scenes, etc can you choose as a vehicle that share the same characteristics?
David Mark’s Anatomy of a Heretic has a ‘green slime that dangles from the roof joists like the hair of drowned sailors’. The slime is old, dead, wet, slimy, algaed, smells rotten, hangs down vertically in strands—a perfect match to dead sailors’ hair, which shares all those characteristics. We get the sense—I’d call it the purport—that the roof is very old and rotten and not one that you’d feel comfortable being under.
Set the character in the scene
Your settings can be metaphors in themselves, even if you don’t say so. If your character is in a cramped, poorly lit room, it could be that she is feeling poorly equipped for life, with troubles pressing in upon her. If he’s atop a hill, looking at a beautiful sunrise, it could be that he’s at the top of his game, just ready for his life to start being wonderful. A secondary character holding a lamp or lit candle can have something to show or teach your character. Do, however, avoid the ‘dark and stormy night’.
Be specific with your meaning
The most wonderful metaphors are not only gorgeous and sensual, time and place specific and match the Voice of their speaker. They are also precisely matched to the meaning they are trying to convey.
In David Mark’s Anatomy of a Heretic, a beautiful, high-class woman walking among crude, low-class sailors is described as ‘like a swan gliding through pondweed’. We get a vivid picture of her gracefulness; she is so refined she doesn’t even notice the sailors. We can almost see them dripping with disgusting slimy pondweed, which doesn’t stick to her, as they swill their ale. The villagers’ brown clothes are ‘all stained the shade of freshly dug graves’. We not only envisage them in colour; we see that they are tired and worn-down, as if ready for the grave.
Evoke emotional truth
You’re putting in the extra work to compose a metaphor because you have something to say. The purport is often some truth or realisation about the tenor that we wouldn’t otherwise have seen. Inviting your reader to follow the logic of your comparison hopefully induces an aha moment where they emotionally experience the truth you were trying to convey.
Extended, implied, mixed metaphors
Extended metaphors are ones that are continued longer than just one phrase. ‘The boss snatched at her report, devoured it as quickly as possible, and then, looking around for more prey, darted across the aisle to her co-worker’s desk.’
Snatched, devoured and prey sustain the image of the boss as a grasping predator. That example is extended over the length of one sentence, but you could also extend a metaphor across a paragraph or even an entire novel. The ‘Eyes of Dr TJ Eckleburg’ billboard in The Great Gatsby is perhaps an allegory for God looking down judgmentally upon the characters as they travel to and from their adulteries.
Implied metaphors use less direct analogies. You could say ‘Harry was like a pufferfish when he got angry’. Or less directly, ‘Harry swelled and, with his prickly spines, wasn’t nearly as approachable as he had been earlier.’ In the second, the word pufferfish isn’t expressly mentioned.
Mixed metaphors should really only be used when you’re trying to be funny. ‘It’s raining turtles and hares.’
There are also absolute, complex, conceptual, conventional, creative, dead, primary, root, submerged, therapeutic, and visual metaphors.
Use scholarly references
Biblical, Greek and Roman mythological or Shakespearean references can be edifying. And if you don’t mind appearing snooty, throwing in the odd French adage or Italian curse adds colour.
 Orson Scott Card
 David Mark, Anatomy of a Heretic
 Rebecca Horsfall, Dancing on Thorns
 David Mark, Anatomy of a Heretic
 F Scott Fitzgerald, The Great Gatsby