Definition · Plain-language
Analogy
An analogy is a comparison that explains or argues for one idea by likening it to another, usually more familiar, thing.
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How an analogy works
An analogy maps the relationship within one pair of ideas onto another pair, helping a reader understand something new through something already known. Saying "a cell is like a factory" works because the parts of a cell perform roles comparable to departments in a factory, so the structure of one explains the structure of the other. Unlike a simile or metaphor, which usually point to a single shared quality, an analogy develops a system of correspondences. This makes it especially useful in teaching, science writing and persuasion, where complex relationships need to be made graspable.
Analogy in argument and reasoning
Beyond explanation, analogies are used to argue: if two cases are alike in relevant respects, what is true of one may be true of the other. This is argument by analogy. Its strength depends on how closely the cases actually resemble each other in the features that matter. A weak or misleading comparison produces the false-analogy fallacy, where surface similarity hides important differences. Lawyers reasoning from precedent, scientists proposing models and writers making a point all rely on analogies that hold up under scrutiny.
Analogy, simile and metaphor
These devices overlap but are not identical. A simile and a metaphor are usually brief figures that liken two things directly, often for vividness. An analogy is broader and more explanatory: it can contain similes or metaphors, but its purpose is to illuminate a relationship or reason through a problem rather than simply decorate. Analogies frequently appear as extended passages and may be entirely literal in tone. Recognising an analogy means looking for a comparison that is doing intellectual work — clarifying, teaching or persuading — not just adding colour.
Key facts
At a glance
- Definition: a comparison that explains one thing by likening it to another
- Purpose: to clarify, teach or build an argument
- Scope: broader than a simile or metaphor; maps a whole relationship
- Example: "the brain is like a computer"
- Argument form: argument by analogy reasons from a familiar case to a new one
- Pitfall: the false-analogy fallacy when key differences are ignored
Common misconceptions
What people often get wrong
Often heard: An analogy is just another word for a simile.
Actually: A simile is one narrow type of comparison using "like" or "as". An analogy is broader: it explains or argues by mapping a whole relationship between two cases, and may use plain literal language rather than a figure of speech.
Often heard: If two things are alike in one way, the analogy proves they are alike in others.
Actually: Argument by analogy is only as strong as the relevant similarities. When important differences are ignored, the comparison commits the false-analogy fallacy, so an analogy can illustrate a point but rarely proves it on its own.
Often heard: Analogies are only used to make writing more colourful.
Actually: Analogies do far more than decorate. They explain difficult concepts, structure scientific models and underpin legal and philosophical reasoning, making them a tool of thought as much as of style.
