Analogy
2 of the 6 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.
What Has Changed in the Last Century
The logic these entries describe is still taught much as they state it: analogy suggests, induction proves, and the biological sense — the bird's wing and the butterfly's, which agree in function but not in ancestry — remains the standard contrast with homology, now explained as convergent evolution and tested against molecular family trees. What has aged is Aiton's chosen illustration. When it wrote in 1910 that Mars's likeness to Earth argued for vegetation and inhabitants while conceding "no one knows," the question was genuinely open; Mariner 4's flyby in 1965 returned images of a cratered desert, and the Viking landers of 1976 confirmed an atmosphere under one-hundredth of Earth's pressure with no clear sign of life. The entry's own warning that analogy "does not give absolute proof" turned out to be the most durable thing in it.
Written for this edition, 2026.