Analogy
2 of the 7 encyclopedias on this shelf carry an entry for Analogy. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
similitude of relations between one thing and other. The thing to which the other is compared is preceded by to or with. When both are mentioned together they are connected by the word between. In logic, the resemblance of relations, first by a meaning given to the word the mathematicians. As more commonly used it is a rewhich an argusemblance of any kind on may be ment falling short of induction is founded. If an invariable conjunction made out between a property erty in the one property in the other, the case and a y, and beargument rises above analogy, basis; comes an induction on a limited been but if no such conjunction has made out, then the argument is one of analogy merely. Metaphor and allegory address the imagination, while analogy are appeals to the reason. The former founded on similarity of appearances, of effects, or of incidental circumstances; essential the latter is built upon more resemblances, which afford a proper basis for reasoning. In biology, an analogy is the relation between parts which agree in function, as the wing of a bird and that of a butterfly, the tail of a whale and that of a fish.
Aiton's Encyclopedia (1910)
a form of reasoning which argues that because objects are alike in many known particulars, they are also alike in some other and unknown particular. An illustration of an argument by analogy is conveniently drawn from the earth and Mars. Both are planets; they revolve about the same sun; they have the same shape; each has an atmosphere; each has a regular succession of seasons. There is an apparent similarity of rainfall, temperature, and the same succession of day and night. Now the earth sustains plant and animal life. Reasoning by analogy, it is urged that Mars is also clothed with vegetation and is inhabited by animals and people. It may be seen readily that analogy is likely to be exceedingly useful in stimulating investigation and in leading to discovery, but that it does not give absolute proof. The analogy seems to be perfect and complete, yet no one knows whether or not Mars is inhabited. 2026 Editor's Note: The article's own example has aged into a caution: reasoning by analogy that Mars must harbor life because it resembles Earth led astronomers of this era to imagine 'canals' and Martians . Spacecraft found a cold, all-but-airless desert instead — though the search for microbial life goes on. (Ed: BR 2026-07-12)