ANALOGY, a correspondence of between one thing and another.
In logic it implies the resemblance of rela tions, a meaning given to the word first by di: mathematicians. To call a country which has sent out various colonies the mother counts implies an analogy between the relation in which it stands to its colonies and that which a mother holds to her children.
As more commonly used it is a resemblance on which an argument falling short of induc tion may be established. Under this meanM.: the element of relation is not especially distin guished from others. "Analogical reasoning . . . . may be reduced to the following for mula: Two things resemble each other in one or more respects; a certain proposition is true of the one, therefore it is true of the other' If a conjunction between a property in the one case and a property in the other finds its place in an established system of correlations, the argument rises above analogy, becoming an in duction on a limited basis; but if no such con junction has been made out, then the argument is one of analogy merely. If two bodies or processes agree closely in certain respects, it is reasonable to suppose that they will also agree in those respects which have been found to be associated therewith. Metaphor and al legory address the imagination, while analog appeals to the reason. The former are founded
on similarity of appearances, of effects or of incidental circumstances; the latter is built up on more essential resemblances which afford a proper basis for reasoning.
In zoology analogy is applied to the resem blance between the entire bodies, or between special structures of organs, in animals of un related types. Thus a whale is analogous in form to a fish: its paddles analogous to the fins of a fish. The wings of an insect are an alogous to those of a bird. Analogy implies a dissimilarity of the ontogenetic and phyla genetic history of two organs, with identity in their use or function, as the legs of a bird or quadruped and those of an insect. These anal ogies are the result of the adaptation of the animal to similar habits, modes of life or like environment, and result in convergence (q.v.), parallelism, and sometimes mimicry (q.v.) (see also HOMOLOGY). Osborn defines analogy in evolution as embracing similar changes due to similar adaptation in function both in homolo gous and in non-homologous organs, both in related and in unrelated animals. The different grades of analogy are shown by Osborn in the following table: