T

SECT. VII.

Of Reasoning by Analogy'.

these two kinds of reasoning which

are direct, we add another of great importance and extent which is indirect and collateral.

The principle, in which this branch of logic has its foundation, is a native bent and propensity of the mind, strengthened by experience and confirmed by habit, by which we are involuntarily led to expect that nature and truth are uniform and analogous throughout the universe-that similar causes of whatever kind will, in similar circumstances, at all times produce similar effects: or, if the causes cannot be known, that similar effects will explain, illustrate, and account for similar effects.

'On the general subject of this chapter, consult Butler's Analogy; Reid's Essays, vol. i. chap. iv.; Stewart's Elements, vol. ii. chap. 4, sect. 2, § 3.

If the liberty of arguing from a similarity of effects be

This principle then resolves itself into similitude, and reason acts upon it, as in all other cases, by comparing and judging. Thus we argue from truths which have been proved by direct reasoning, or which are obvious to simple apprehension, to others which are similar in cause or in effect; and if, upon comparing and judging, the principle will bear us out, we conclude the latter to be also true; a conclusion which will supply us with a kind and degree of truth sufficient for most of the uses and purposes of human life.

This method of reasoning is Analogy, which according to Quintilian, is "to refer a thing that is doubtful, to something similar and different, that uncertainties may derive their proof from certainties"."

This kind of reasoning has a more permanent and certain foundation than perhaps may appear to some upon a superficial esti

once denied us, all experimental philosophy will be in a manner useless. Jones's Philosophy, p. 119.

* Analogiæ hæc vis est, ut id, quod dubium est, ad aliquod simile, de quo non quæritur, referat, ut incerta certis probetur. Quintilian. Inst. Orat. lib. i. cap. 6.

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mate of that similitude on which it rests. "This is not," says the excellent Bishop Browne, an appearing and metaphorical similitude; it is the substituting the idea or conception of one thing to stand for and represent another, on account of a true resemblance and correspondent reality in the very nature of the things compared. It is defined by Aristotle, an equality or parity of reasoning; though, in strictness of speaking, the parity of reasoning is rather built on the similitude and analogy, and consequent to them, than the same with them"."

The result of this reasoning is however not properly conviction; it is only strong presumption at best; and, from the view of the truths we know, arises an opinion concerning those we do not know, which opinion will of course vary in the degrees of its force almost from the point of absolute certainty through the whole scale of probabilities, down to the confines of doubt and conjecture-according to the nature of the

· Ἡ ἀναλογία ἰσότης ἐπὶ λόγω. Ethic. Nicom. lib. v. сар. 3.

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Bp. Browne's Divine Analogy, p. 2.

truths from which we reason-according to their greater or less extent and-according as the cases and instances compared are more or less similar.

Analogy is a species of logic on which the Stagyrite has been as frugal of his philosophy, as he was upon induction. It is however a method of reasoning of most useful and important application and almost of universal extent in life.

It is the business of the first logic to convey truth' and information to the mind, easy in its application and obvious in its conclusion. And besides this advantage, resulting from its plainness and familiarity (an advantage which the ablest philosophers and the divinest teachers have been careful to improve), it has other privileges. Many truths, divine and human, of the last importance to men are incapable both of direct proof and direct

The #apádyμa, of which he speaks in the twenty-fifth chapter of the second book of the Prior Analytics in a very cursory way, is indeed something like analogy, TÚTO DE TISIC ἐκ τῶν ὁμοίων—φανερὸν ἦν ὅτι τὸ παράδειγμά ἐτιν, ὅτε ὡς ὅλον πρὸς μέρος, ὅτε ὡς μέρος πρὸς ὅλον, ἀλλ ̓ ὡς μέρος πρὸς μέρος, ὅταν ἄμφω μὲν ᾖ ὑπὸ τὸ αὐτὸ, γνώριμον δὲ θάτερον.

communication, and can only be evinced and conveyed to the understanding, by this indirect and collateral channel. Many which can be directly proved and directly conveyed, it illustrates with clearer and fuller light, and sets them in a point of view easier to be seen and apprehended by us.

But analogy has also a scientific use which is conspicuously displayed, when it acts as a necessary supplement and auxiliary to inductive reasoning, without which, this useful part of logic would remain very defective and confined. When the philosopher has founded a general truth or proposition upon a certain number of particular comparisons, it is by the help of analogy that he gives it an extent over all similar instances throughout the universe, till it may happen to be contradicted by one, in which it is found to fail. So that by analogy the whole province of truth is facilitated, illustrated and enlarged, and widened beyond the strict and proper limits both of inductive and syllogistic reasoning.