ANALOGY (Gk. ima2o)ia, anal-ogia, equality of ratios). In general, an agreement or corres pondence in certain respects between things in other respects different. Euclid employed it to signify proportion, or the equality of ratios, and it has retained this sense in mathematics; but it is a term little used in the exact sciences, and of very frequent use in every other department of knowledge and in human affairs. In grammar we speak of the analogy of language: i.e., the correspondence of a word or phrase with the genius of the language, as learned from the man ner in which its words and phrases are ordi narily formed. Analogy, in fact, supposes a rule inferred from observation of instances, and is the application of this rule to other instances not pre cisely, but somewhat, similar. We venture upon this application with more or less confidence, according to the degree of ascertained similarity, and according to the extent of observation from which our knowledge of the rule has been de rived. John Stuart AIM, in his Logic, states the formula of analogy in this way: "Two things resemble each other in one or more re spects; a certain proposition is true of the one, therefore it is true of the other." What makes analogical reasoning successful at all is the fact that superficial resemblances often point to fun damental identity in type. Analogical reasoning is the assumption of a deeper significance in similarities than our knowledge of the facts warrants. When this assumption is justified by the event, the analogy has been fruitfully sug gestive; when it is not, the analogy has been misleading. Even when analogy leads to dis covery, it does this merely by suggestiveness; the final establishment of the truth analogically adumbrated is never accomplished by analogy, but by some stricter logical method. Thus, rea soning from analogy indeed warrants only prob able conclusions; but the probability may be come of a very high degree, and in the affairs of life we must often act upon conclusions thus attained. Reasoning from analogy, however, re
quires much caution in the reasoner. Yet even when its conclusions are very uncertain, they often serve to guide inquiry and lead to dis covery. :Many of the most brilliant discoveries recently made in natural science were the result of investigations thus directed. In law, reason ing from analogy must often, to a certain extent, be admitted in the application of statutes to particular cases. Upon similar reasoning, the practice of medicine very much depends. In literary criticism, it is also often necessary for purposes of interpretation, the sense of the auth or in a passage somewhat obscure being in some measure determined according to passages in which lie has expressed himself more clearly. The application of this rule to the interpretation of Scripture is a point of difference between Protestants and Catholics, the latter insisting upon the interpretation of difficult passages by ecclesiastical tradition and authority. Prot estant theologians have very generally employed, with reference to this rule of interpretation, the phrase "analogy of faith," deriving it from Romans xii. 16; but the meaning of the ex pression in that verse is disputed. (See PHONET IC Laws.) The opposite of analogy is anomaly (Gk. irregularity) ; and this term is used not only in grammar, but with reference to objects of natural history which in any respect are ex ceptions to the ordinary rule of their class or kind. In physiology, analogy is similarity of function between organs which are structurally or morphologically different; e.g., the tail of a fish and that of a whale are analogous organs; in this usage analogy is opposed to homology, which refers to the structural similarity of or gans that may even perform different functions; e.g., the wing of a bird and the arms of a man.