ANALOGY, in Philosophy, a certain relation and agreement between two or more things, which in other respects are entirely different. There is likewise an analogy between things that have some conformity or resemblance to one another; for example, between animals and plants; but the analogy is still stronger between two different species of certain animals. Analogy enters much into all our reasoning, and serves to explain and illustrate. A great part of our philosophy, indeed, has no other foundation than analogy.

“It is natural to mankind,” says Dr Reid,“to judge of things less known, by some similitude, real or imaginary, between them and things more familiar or better known. And where the things compared have really a great similitude in their nature, when there is reason to think that they are subject to the same laws, there may be a considerable degree of probability in conclusions drawn from analogy. Thus, we may observe a very great similitude between this earth which we inhabit, and the other planets, Saturn, Jupiter, Mars, Venus, and Mercury. They all revolve round the sun, as the earth does, although at different distances and in different periods. They borrow all their light from the sun, as the earth does. Several of them are known to revolve round their axis like the earth, and, by that means, must have a like succession of day and night. Some of them have moons, that serve to give them light in the absence of the sun, as our moon does to us. They are all, in their motions, subject to the same law of gravitation as the earth is. From all this similitude, it is not unreasonable to think that those planets may, like our earth, be the habitation of various orders of living creatures. There is some probability in this conclusion from analogy.”

“But it ought to be observed, that as this kind of reasoning can afford only probable evidence at best, so, unless great caution be used, we are apt to be led into error by it.”—“No author has made a more just and a more happy use of this mode of reasoning than Bishop Butler, in his Analogy of Religion, Natural and Revealed, to the Constitution and Course of Nature. In that excellent work, the author does not ground any of the truths of religion upon analogy, as their proper evidence; he only makes use of analogy to answer objections against them. When objections are made against the truths of religion, which may be made with equal strength against what we know to be true in the course of nature, such objections can have no weight.”

“Analogical reasoning, therefore, may be of excellent use in answering objections against truths which have other evidence. It may likewise give a greater or a less degree of probability in cases where we can find no other evidence. But all arguments drawn from analogy are still the weaker, the greater disparity there is between the things compared; and therefore must be weakest of all when we compare body with mind, because there are no two things in nature more unlike.”

“There is no subject in which men have always been so prone to form their notions by analogies of this kind, as in what relates to the mind. We form an early acquaintance with material things by means of our senses, and are bred up in a constant familiarity with them. Hence we are apt to measure all things by them, and to ascribe to things most remote from matter the qualities that belong to material things. It is for this reason that mankind have, in all ages, been so prone to conceive the mind itself to be some subtile kind of matter; that they have been disposed to ascribe human figure and human organs, not only to angels, but even to the Deity.” (Essays· on the Intellectual Powers.) There are some profound observations on the subject of analogy, and on the difference between the evidence of experience and that of analogy, in Stewart’s Philosophy of the Mind, vol. ii. chap. ii. sect. 4.

Analogy, in Grammar, is the correspondence which a word or phrase bears to the genius and received forms of any language.