What is Analogy?

Legal Definition
Analogy (from Greek ἀναλογία, analogia, "proportion") is a cognitive process of transferring information or meaning from a particular subject (the analogue or source) to another (the target), or a linguistic expression corresponding to such a process. In a narrower sense, analogy is an inference or an argument from one particular to another particular, as opposed to deduction, induction, and abduction, where at least one of the premises or the conclusion is general. The word analogy can also refer to the relation between the source and the target themselves, which is often, though not necessarily, a similarity, as in the biological notion of analogy.

Analogy plays a significant role in problem solving, as well as decision making, perception, memory, creativity, emotion, explanation, and communication. It lies behind basic tasks such as the identification of places, objects and people, for example, in face perception and facial recognition systems. It has been argued that analogy is "the core of cognition". Specific analogical language comprises exemplification, comparisons, metaphors, similes, allegories, and parables, but not metonymy. Phrases like and so on, and the like, as if, and the very word like also rely on an analogical understanding by the receiver of a message including them. Analogy is important not only in ordinary language and common sense (where proverbs and idioms give many examples of its application) but also in science, philosophy, and the humanities. The concepts of association, comparison, correspondence, mathematical and morphological homology, homomorphism, iconicity, isomorphism, metaphor, resemblance, and similarity are closely related to analogy. In cognitive linguistics, the notion of conceptual metaphor may be equivalent to that of analogy.

Analogy has been studied and discussed since classical antiquity by philosophers, scientists, and lawyers. The last few decades have shown a renewed interest in analogy, most notably in cognitive science.
-- Wikipedia
Legal Definition
Comtruction. The similitude of relations which exist between things compared.

2. To reason analogically, is to draw conclusions based on this similitude of relations, on the resemblance, or the connexion which is perceived between the objects compared. "It is this guide," says Toollier, which leads the law lawgiver, like other men, without his observing it. It is analogy which induces us, with reason, to suppose that, following the example of the Creator of the universe, the lawgiver has established general and uniform laws, which it is unnecessary to repeat in all analogous cases." Dr. Civ. Fr. liv. 3, t. 1, c. 1. Vide Ang. on Adv. Enjoym. 30, 31; Hale's Com. Law, 141.

3. Analogy has been declared to be an argument or guide in forming legal judgments, and is very commonly a ground of such judgments. 7 Barn. & Cres. 168; 3 Bing. R. 265; 8 Bing R. 557, 563; 3 Atk. 313; 1 Eden's R. 212; 1 W. Bl. 151; 6 Ves. jr. 675, 676; 3 Swanst. R. 561; 1 Turn. & R. 103, 338; 1 R. & M. 352, 475, 477; 4 Burr. R. 1962; 2022, 2068; 4 T. R. 591; 4 Barn. & Cr. 855; 7 Dowl. & Ry. 251; Cas. t. Talb. 140; 3 P. Wms. 391; 3 Bro. C. C. 639, n.
-- Bouviers Law Dictionary
Legal Definition
In logic. Identity or similarity of proportion. Where there is no, precedent in point, in cases on the same subject, lawyers have recourse to cases on a different subject-matter, but governed by the same general principle. This is reasoning by analogy. Wharton.
-- Black's Law Dictionary