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Again, likeness or resemblance, τὸ ὅμοιον, between two things suggests or implies a common possibility; if one thing can be done, the probability is that anything else like it can be done equally.

This is a variety of the argument from analogy. We have a tendency, which appears to be natural and instinctive, to infer from any manifest or apparent resemblance between two objects, that is, from certain properties or attributes which they are seen or known to possess in common, the common possession of other properties and attributes, which are not otherwise known to belong to them, whereby we are induced to refer them to the same class. So here, the likeness of two things in certain respects, is thought to imply something different, which is also common to both; a common capacity or possibility. The argument being here applied solely to the use of Rhetoric, the things in question are rather actions and their consequences than facts and objects: if it has been found possible to effect something, to gain some political advantage for instance, in several previous cases, we argue that in the similar, parallel case which is under consideration, the like possibility may be expected.

This however, though the popular view of the argument from analogy, and the ordinary mode of applying it, is not, strictly speaking, the right application of the term. Analogy, τὸ ἀνάλογον, is arithmetical or geometrical proportion, and represents a similarity, not between objects themselves, but between the relations of them. See Sir W. Hamilton, Lect. on Logic, Vol. 11. p. 165—174, Lect. XXXII, and on this point, p. 170. Whately (Rhet. p. 74, c. 1), “Analogy, being a resemblance of ratios, that should strictly be called an argument from analogy, in which the two cases (viz. the one from which, and the one to which we argue) are not themselves alike, but stand in a similar relation to something else; or, in other words, that the common genus that they both fall under, consists in a relation.” This he illustrates by two examples of analogical reasoning. One of them is, the inferences that may be drawn as to mental qualities and the changes they undergo, from similar changes (i.e. relations) in the physical constitution—though of course there can be no direct resemblance between them. Hamilton's illustration of analogy proper is derived directly from a numerical proportion: that of analogy in its popular usage is, “This disease corresponds in many symptoms with those we have observed in typhus fevers; it will therefore correspond in all, that is, it is a typhus fever,” p. 171.

Buther's Analogy of Natural and Revealed Religion to the constitution and course of Nature may be regarded as an analogy of relations between them and God the author of both, in the proper sense of the word, though in his Introduction he twice appears to identify analogy with mere likeness or similarity.

Lastly, the logical description of Analogy is to be found in Thomson's Law of Thought, § 121, ‘Syllogism of Analogy’, p. 250, seq. The author's definition is, p. 252, “the same attributes may be assigned to distinct but similar things, provided they can be shewn to accompany the points of resemblance in the things, and not the points of difference.” Or ‘when the resemblance is undoubted, and does not depend on one or two external features’), “when one thing resembles another in known particulars, it will resemble it also in the unknown.”

On the different kinds of ὁμοίοτης and ὅμοια, consult Metaph. Δ 11, 1018 a 15, with Bonitz' note, and Ib. I 3, 1054 b 3, seq., also Top. A 17, on its use as a dialectical topic.

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