A metaphor says that one thing is another: “Juliet is the sun.” An analogy shows how two things work alike, part by part, so that something familiar explains or argues for something less familiar: the heart works like a pump, because both push liquid through a closed loop of pipes and both fail when the pressure drops. A metaphor is a figure of speech. An analogy is a line of reasoning, and it often uses metaphors and similes along the way.
The quickest test is whether you could check it. Nobody can prove that Juliet is or isn't the sun; the line works or it doesn't. An analogy makes claims about structure, so a reader can test it point by point and find where it breaks. That is what makes analogies useful for explaining and arguing, and what makes them easy to attack.
Metaphor, simile and analogy compared
Hold the subject still and the three come apart. Here is one heart, compared three ways:
- Metaphor: Before the verdict, his heart was a drum.
- Simile: Before the verdict, his heart beat like a drum.
- Analogy: The heart works like a pump. Its chambers fill and squeeze, valves keep the blood moving one way, and when the pressure drops, everything downstream goes short.
The metaphor and the simile carry one quality, the pounding, and tell you how the moment felt. The analogy starts explaining at its second sentence: chambers, valves and pressure each match a part of a pump, and a doctor could check every one of them.
| Device | What it does | Usual length | Example |
|---|---|---|---|
| DeviceMetaphor | What it doesCalls one thing another to transfer a quality | Usual lengthA word or phrase | Example“It is the east, and Juliet is the sun.” (Romeo and Juliet, c. 1595) |
| DeviceSimile | What it doesCompares openly, with “like” or “as” | Usual lengthA phrase or clause | Example“I wandered lonely as a cloud” (Wordsworth, 1807) |
| DeviceExtended metaphor | What it doesKeeps one metaphor going and develops it | Usual lengthSeveral lines to a whole poem | Example“‘Hope’ is the thing with feathers” (Dickinson, published 1891) |
| DeviceAnalogy | What it doesMaps how two things work alike to explain or prove a point | Usual lengthA sentence to several paragraphs | ExamplePaley's watch and its maker (Natural Theology, 1802) |
| DeviceAllegory | What it doesTells a whole story in which characters and places stand for ideas | Usual lengthA passage to a whole book | ExamplePlato's cave; Bunyan's The Pilgrim's Progress (1678) |
What a metaphor is
The word comes from the Greek metapherein, “to carry over”: a metaphor carries a name, and everything attached to it, from one thing to another. Aristotle defined it in the Poetics as “the application of an alien name by transference” (S. H. Butcher's translation, 1895), and he rated the skill above all others in a writer: “the greatest thing by far is to have a command of metaphor,” because “to make good metaphors implies an eye for resemblances.”
A metaphor doesn't announce itself or explain itself. When Romeo says Juliet is the sun, he doesn't list the ways she resembles a star; the reader supplies warmth, light and the fact that the rest of the night now revolves around her. The critic I. A. Richards, in The Philosophy of Rhetoric (1936), called the two halves the tenor (Juliet, the subject) and the vehicle (the sun, the image that carries meaning to it).
Life's but a walking shadow, a poor player
That struts and frets his hour upon the stage
Two metaphors in two lines: life as a shadow, then as a bad actor whose part is soon over. Neither is argued. They land because the reader feels the fit at once.
Everyday language is full of metaphors so worn that nobody notices them: the leg of a table, a bottleneck in production, grasping an idea, a heated debate. These dead metaphors are fine in plain prose. Trouble starts when two live ones collide in the same sentence, as in “we'll have to iron out the bottleneck before it snowballs.”
Similes and extended metaphors
A simile makes the comparison explicit with “like” or “as”: Wordsworth's “I wandered lonely as a cloud” (1807). Because it admits to being a comparison, a simile asks less of the reader and is easier to qualify. An extended metaphor keeps one comparison going and develops it. Emily Dickinson's poem, first published in 1891, opens with the image and stays with it to the end, through the bird's song, the storm and the cold:
“Hope” is the thing with feathers
That perches in the soul
Jaques's “All the world's a stage” speech in As You Like It works the same way, walking one metaphor through seven ages of a life. An extended metaphor is the point where metaphor starts to look like analogy, because the parts begin to line up. The difference is purpose: Dickinson isn't explaining how hope works or proving anything about it.
What an analogy is
Analogy comes from the Greek analogia, “proportion”: A is to B as C is to D. Aristotle counted one kind of metaphor as analogy, “by analogy, that is, proportion,” and his own example shows the mechanics: old age is to life as evening is to day, so a poet can call old age “the evening of life.” An analogy states that proportion openly and does something with it.
Analogies do one of two jobs. Some explain: they borrow the structure of something the reader knows to make an unfamiliar system graspable. Others argue: they claim that because two things are alike in some ways, what's true of one is true of the other. The second kind persuades only as far as the likeness holds.
Analogies that explain
Electricity. Voltage is like water pressure in a pipe, current like the amount of water flowing past a point each second, and resistance like a narrow section of pipe. Turn up the pressure and more water flows; narrow the pipe and less does.
Databases. An index works like the index at the back of a book. Instead of reading every page to find “photosynthesis,” you look it up, get a page number and go straight there. Like a book index, it costs space and has to be updated whenever the pages change.
Immunology. A vaccine works like a wanted poster. It shows the immune system what the intruder looks like before the intruder arrives, so the response is faster when it does.
Notice that the database analogy names a limit: an index costs space and needs upkeep. Saying where an analogy stops working keeps an explanation honest, and it stops the reader carrying the comparison further than it goes.
Analogies that argue
The most famous argument by analogy in English opens William Paley's Natural Theology (1802). Find a stone on a heath and you might suppose it had always been there. Find a watch, with parts fitted together for a purpose, and you would reason differently:
In crossing a heath, suppose I pitched my foot against a stone, and were asked how the stone came to be there; … But suppose I had found a watch upon the ground, and it should be inquired how the watch happened to be in that place; … the inference, we think, is inevitable, that the watch must have had a maker
The argument runs: a watch shows design and has a designer; living things show design; so living things have a designer too.
The attack on an argument like this goes after the likeness itself. David Hume had already done it in Dialogues Concerning Natural Religion (published 1779), where the skeptic Philo argues that the universe is too unlike a machine for the comparison to carry weight, and that other comparisons, such as a growing plant or an animal, fit the evidence just as well. More than half a century after Paley, Charles Darwin used an analogy of his own, from breeders to nature:
As man can produce and certainly has produced a great result by his methodical and unconscious means of selection, what may not nature effect?
A breeder picks which animals reproduce and changes a breed in a few generations; nature, with far more time, does the picking through survival. In later editions Darwin changed “nature” to “natural selection,” tightening the comparison to the mechanism he meant.
For more ways comparisons work in an argument, see persuasive techniques and the comparison devices in the rhetorical devices glossary.
How to tell them apart
When you can't decide what a comparison is, ask four questions.
- Could you check it? If the comparison makes claims about how something works that a reader could test, it's an analogy. If it only transfers a feeling or quality, it's a metaphor or simile.
- Is there a “so”? Analogies lead somewhere: so the heart can fail like a pump, so living things must have a maker. A metaphor rests on its image.
- How many parts line up? A metaphor usually maps one quality. An analogy maps several: pressure to voltage, flow to current, pipe width to resistance.
- Does it say “like” or “as”? That separates a simile from a metaphor, but not either of them from an analogy, which can use both words or neither.
Metaphor
- A figure of speech: one thing is called another
- Works through a single image the reader feels at once
- Usually a word or a phrase
- Can't be proved wrong, only weak or mixed
- Its job is meaning, mood and emphasis
Analogy
- A line of reasoning: two things work alike
- Lines up several parts, often openly
- A sentence to several paragraphs
- Can be tested and shown to break
- Its job is explaining or arguing
False analogy and weak comparisons
A false analogy, also called a weak or faulty analogy, is an argument that treats two things as alike in the way that matters when they aren't. The two things usually do share something. The flaw is that the shared feature isn't the one the conclusion depends on, so the useful move is to name the exact point where the parallel breaks.
“A novel is like a building: nobody lays bricks without a blueprint, so every novelist has to outline first.” Both are big structures made in stages. The parallel breaks at the cost of starting over: a wall can't be knocked down and rebuilt for free, and a chapter can. That is one reason many novelists discover the plan by drafting.
“A team is like a family, so people should stay late when the team needs them.” Teams and families both rely on loyalty. The parallel breaks at the terms: a job is an agreement to work set hours for pay, and a family isn't.
“Writing is like riding a bike: once you learn, you never lose it.” Both are learned skills. The parallel breaks at what the skill is made of: balance is a motor skill that lasts, while writing well depends on reading, practice and knowledge of a subject, all of which fade without use.
To test any analogy, yours or an opponent's, write down the conclusion, list the features of the familiar thing that make the conclusion true there, and check each one against the new case. One missing feature that the argument depends on is enough to sink it.
To check a long draft for both problems, ask the Strokes Assistant to review it for mixed metaphors and for analogies that switch sources halfway through.
How to write an analogy for a newcomer
Explanatory analogies matter most when you're writing for people outside your field: a grant panel, a general reader, a client, a new team member. These steps keep the analogy doing the explaining rather than becoming one more thing to decode.
- Start from what the reader already knows
Pick a source from the reader's life, not yours. Plumbing works for most readers; a comparison to a sport can lose anyone who doesn't follow it.
- Map three or four parts
Write the correspondences down before you draft: index = book index, row = page, query = the word you look up. If you can only map one part, use a plain explanation or a metaphor instead.
- Say where it breaks
One sentence is enough: “Unlike a book index, a database index has to be rebuilt every time the data changes.” It stops the reader carrying the comparison too far.
- Use it once, then return to the real thing
An analogy is a door into the subject, not a place to stay. After a paragraph, switch to the actual terms the reader will need.
- Test it on someone outside the field
Ask them to explain the idea back in their own words. If they describe the analogy instead of the idea, the comparison is doing too much.
Some analogies outlive their explanation and turn into everyday terms. In a 1992 conference report, the programmer Ward Cunningham put it this way: “Shipping first time code is like going into debt.” The comparison mapped neatly (shortcuts are the loan, slower future work is the interest, rewriting is the repayment), and “technical debt” is now a standard term in software teams.
Practice: metaphor, simile or analogy?
Decide what each line is, then check the answers.
- The city is a beehive at rush hour.
- She argued like a lawyer with an hour left on the meter.
- A firewall is like a building's security desk: it checks who is entering, turns away anyone not on the list and logs every visit.
- Grief is a house where the clocks have all stopped, and every room is a different year.
- Since a ship needs one captain, a company should never have two CEOs.
- His promises were paper boats.
- Editing a draft is like pruning a tree: you cut back healthy branches so the strongest ones get the light.
- The interview went off like a firework, bright and over in seconds.
- Metaphor: the city is called a beehive.
- Simile: “like a lawyer.”
- Explanatory analogy: three parts are mapped (checking, refusing, logging).
- Extended metaphor: the image is developed, but nothing is explained or argued.
- Argument by analogy, and a weak one. It breaks at the reason a ship has one captain: at sea, one person has to give orders in seconds, and most company decisions aren't made that way, which is why some companies do run with co-CEOs.
- Metaphor.
- Explanatory analogy: cutting healthy branches maps to cutting good but unneeded material.
- Simile, extended a little.
Word analogies on tests
Tests use “analogy” for a different exercise. A word analogy is a puzzle, written hand : glove :: foot : sock and read “hand is to glove as foot is to sock.” It checks whether you can name a relationship, not whether a comparison explains anything. The method is to state the relationship in the first pair precisely, then find the pair that shares it. Analogy questions were a staple of the SAT until the verbal analogy section was dropped from the revised test in 2005, and they still appear in many aptitude tests and classrooms.
| Relationship | Example |
|---|---|
| RelationshipPart to whole | Examplepage : book :: brick : wall |
| RelationshipTool to user | Examplescalpel : surgeon :: chisel : sculptor |
| RelationshipCause to effect | Exampledrought : famine :: spark : fire |
| RelationshipDegree | Examplewarm : hot :: damp : soaked |
| RelationshipSynonym | Examplebrave : valiant :: tired : weary |
| RelationshipAntonym | Examplegenerous : stingy :: candid : evasive |
| RelationshipFunction | Examplepen : write :: knife : cut |
One habit from the puzzle does carry over to prose. Before you use an explanatory analogy, try stating it in that four-slot form. If you can't fill the slots, the comparison may be a loose metaphor posing as an explanation.
Frequently asked questions
Is an analogy a metaphor?
Not quite. A metaphor is a figure of speech that calls one thing another to transfer a quality. An analogy is a comparison worked out as reasoning: it shows how two things function alike in order to explain or argue. An analogy can contain metaphors, and Aristotle treated proportional metaphor as a kind of analogy, but most analogies spell out the likeness while metaphors leave it implied.
What is the difference between an analogy and a simile?
A simile compares two things with “like” or “as” to describe one of them: “lonely as a cloud.” An analogy compares how two things work in order to explain or prove something, and it may or may not use “like.” A simile usually maps one quality; an analogy maps several parts and draws a conclusion from the match.
How is an extended metaphor different from an analogy?
Both develop a comparison over several lines. An extended metaphor does it for meaning and feeling, as Dickinson does with hope as a bird. An analogy does it to explain or argue, and it can be tested: you can ask whether each mapped part really behaves the same way. If the comparison leads to a “so,” it is working as an analogy.
