BOOK II. of the passions.
PART I. of pride and humility
SECTION XII. Of the pride and humility of animals
It has been proved in the foregoing that the causes of pride and humility cannot excite the passions unless they are related to the self and produce an independent pleasure or pain. This is the only thing all such causes have in common, "and consequently is the quality, by which they operate." Moreover, "the most considerable causes of these passions are really nothing but the power of producing either agreeable or uneasy sensations; and therefore that all their effects, and amongst the rest pride and humility, are deriv’d solely from that origin." Hume can find on viable objections to this view, and because it is so simple, natural, and well-proved, it "cannot fail to be receiv’d [i.e., accepted] by philosophers."
In anatomy, experiments on other animals confirm those made on human beings, given the similarity of structures between us, so "whatever we discover to be true of the one species, may be concluded without hesitation to be certain of the other." The analogy may break down at times, but in most basic respects we are very similar, and the explanations that work for one should also work for the other. This comparative method can be applied to the "present anatomy of the mind" as well as to that of the body.
First, the correspondence between the passions of the two will be shown; then those of the causes that produce the passions.
Nearly every species of creature, especially the "nobler kind" shows "many evident marks of pride and humility." Many examples are given. In most cases, the vanity is with respect to those characteristics that distinguish the species, such as the swiftness of horses." Those animals that approach human beings take pride in the approval of humans, "independent of every other consideration." They also take pride only in the caresses of those "they know and love; in the same manner as that passion is excited in mankind."
The causes are the same as with us, taking into account "our superior knowledge and understanding." (I.e., they have little sense of virtue or vice, easily lose track of blood relation, etc., so the causes must be placed solely in their bodies, rather than in their minds or in external objects.) Beauty, strength, swiftness, "or some other useful or agreeable quality" is the cause.
Do they operate in the same way? The rules of analogy "justly" lead us to expect that they do, and if we find an explanation that does not transfer, we must suspect that it is without foundation.
The association of ideas works the same in both humans and other animals. In the case of contiguity, it can be seen from the behavior of a dog, who forgets where he has buried a bone, but upon being brought to the place makes an easy transition to the thought of the bone. It behaves the same way at the site of a beating it had suffered. Resemblance is less of a factor, but it does have a role to play in causation, "of which all animals shew so evident a judgement," so that all three relations "operate in the same manner upon beasts as upon humans."
The animals also shows evidence of relations of impressions, so that "their minds are frequently convey’d thro’ a series of connected emotions." For example, grief in a dog is easily converted into anger.
Summary: all the internal principles (of association) are the same in the two cases, as are the causes. So "we may justly conclude, that these causes operate after the same manner thro’ the whole animal creation." The simplicity of Hume’s "hypothesis" makes it so universally applicable, "which must not only be allow’d to be a convincing proof of its veracity," but is the basis for rejecting all rival systems.