ANALOGY, in Philosophy, a certain relation, corres pondence, or agreement, between several things in some respects, which yet differ in others. It includes, there fore, a resemblance joined with some diversity ; and, according to the schoolmen, its foundation is laid in the proportion of several things, contemplated as proceed ing from different considerations. They treat of three kinds of it, that of inequality, of attribution, and of pro portionality ; but it is of more benefit to consider ana logy in reference to its degrees than its genera.
The second law of philosophising laid down by sir Isaac Newton, recommends drawing conclusions from analogy where the resemblance between the things com pared is strong. " Of natural effects of the same kind," says that law, " the same causes are to be assigned as far as it can be done. As of respiration in a man and in a beast ; of the descent of stones in Europe, and in America; of light in a culinary fire, and in the sun ; and of the reflection of light in the various planets." Where the analogy is so very manifest, as in the cases here adduced, the conclusion drawn from it approaches to absolute certainty ; and in many cases we have no bet ter way of reasoning from what is known to what is un known. The arguments by which sir Isaac Newton es tablishes the truth of the system of universal gravita tion are precisely of this sort. He proves, that the pla nets in their deflections towards the sun are all governed by the same analogy that is observable in the deflec tions of the earth towards the sun, and of the moon to wards the earth, as well as of a body projected obliquely at the earth's surface towards its centre : whence he infers, with the force of demonstration, that all these de flections spring from the same cause, or are governed by one and the same law, to wit, the power of gravita tion, by which a heavy body, when unsupported, natu rally falls to the ground.
But there is a natural proneness in men to carry argu ments drawn from analogy too far ; so that this law of philosophising requires to be interpreted with more strictness, and its abuses more carefully guarded agains! than any other. That principle (,1 human thought by
which we ffirm numerous combinations among the ob jects of our knowledge, according to real or resemblances, is continually prompting us to carry com parison farther than the nature of things will \Ve are always apt to judge of things little n by those with which we are familiar ; and to trace simili tudes, which, though often the mere suggestions of our imagination, we are apt to mistake for of reason. Natural historians are fond of tracing an analogy between the three kingdoms of nature, the animal, the vegetable, and the mineral. The analogy between ani mals and vegetables is doubtless, in many cases, very striking. They are both of an organised or vascular struc ture ; both grow and expand from minute germs by as similating nourishment from the different elements ; both are capable of reproducing their kinds, by the generation of ova or seeds. These, and various other points of analogy between plants and animals, are suffi ciently striking, and have been admitted by all ; but na turalists have not stopped here. Actuated by the Wild ness for carrying analogy to its utmost limit, they have extended to vegetables properties which can only be long to sentient beings. It is thus that they have as cribed to plants, a state of sleep and of wakefulness, a power of voluntary motion, and a capacity of avoiding danger, till at length they have not stopped short of ascri bing to them actual sensibility and perception, and have elevated them to the very- rank of living creatures.
" Trees," says Mr White, " are animated, they have their food, their enjoyments, their grief, their health, their illness, their watching, their sleep, their emana tions, their absorptions, their infancy, their growth, their puberty, their manhood, and their love. The man who does not find in animals, younger brothers, and in plants cousins, more or less removed, is unacquainted with his own nature, and is devoid of the elements of morality."— On the gradations in Man, p. 6.