An analogy is a comparison between two different things, in order to highlight some form of similarity.
Analogies are often used to explain new or complex concepts by showing the similarity between something familiar and something else.
- In linguistics, an analogy can be a spoken or textual comparison between two words (or sets of words) to highlight some form of semantical similarity between them. Linguistical analogies can be used to strengthen political and philosophical arguments, even when the semantical similarity is weak or non-existent (if crafted carefully for the audience).
- An analogy can also be the linguistical process that reduces word forms perceived as irregular by remaking them in the shape of more common forms that are governed by rules. For example, the English verb help once had the preterite holp and the past participle holpen. These obsolete forms have been discarded and replaced by helped by the power of analogy. However, irregular forms can sometimes be created by analogy; one example is the American English past tense form of "dive": "dove", formed on analogy with words such as drive-drove.
- Neologisms can be formed by analogy with existing words. A common example is software, formed by analogy with hardware. Another example is the humorous term underwhelm, formed by analogy with overwhelm.
Some types of analogies can have a precise mathematical formulation through the concept of isomorphism.
- See also: Analogy (biology)
In anatomy, two anatomical structures are considered to be analogous when they serve similar functions but are not evolutionarily related, such as the legs of vertebrates and the legs of insects. Analogous structures are the result of convergent evolution and should be contrasted with homologous structures.
In law, analogy is used to resolve issues on which there is no previous authority. A distinction has to be made between analogous reasoning from written law and analogy to precedent case law.
Analogies from codes and statutes
In civil law systems, where the preeminent source of law are legal codes and statutes, a lacuna arises when a specific issue is not explicitly dealt with in written law. Judges will try to identify a provision whose purpose applies to the case at hand. That process can reach a high degree of sophistication, as judges sometimes not only look at specific provision to fill lacunae (gaps), but at at several provisions (from which an underlying purpose can be inferred) or at general principles of the law to identify the legislator's value judgement from which the analogy is drawn.
Analogies from precedent case law
By contrast, in common law systems, where precedent cases are the primary source of law, analogies to codes and statutes are rare (since those are not seen as a coherent system, but as incursions into the common law). Analogies are thus usually drawn from precedent cases: The judge finds that the facts of another case are similar to the one at hand to an extent that the analogous application of the rule established in the previous case is justified.
The United States-based SAT college entrance test includes "analogy" questions that ask for comparisons between analogies: A is to B as C is to what? For example:
- Hand is to palm as foot is to ____?
These questions are usually given in the format:
- HAND : PALM : : FOOT : ____
- Dictionary of the History of Ideas: (http://etext.lib.virginia.edu/cgi-local/DHI/dhi.cgi?id=dv1-09) Analogy in Early Greek Thought
- Dictionary of the History of Ideas: (http://etext.lib.virginia.edu/cgi-local/DHI/dhi.cgi?id=dv1-10) Analogy in Patristic and Medieval Thought
Holyoak, K.J. et. al. (1996). Mental Leaps: Analogy in Creative Thought. Cambridge, Massachusetts, The MIT Press.