Hume has a biological, evolutionist intuition on the nature of passions in human beings:
… we must first shew the correspondence of passions in men and animals, and afterwards compare the causes, which produce these passions.
He operates by relying on similarity, through resemblance:
The causes of these passions are likewise much the same in beasts as in us, making a just allowance for our superior knowledge and understanding. Thus animals have little or no sense of virtue or vice; they quickly lose sight of the relations of blood; and are incapable of that of right and property; For which reason the causes of their pride and humility must lie solely in the body, and can never be plac’d either in the mind or external objects. But so far as regards the body, the same qualities cause pride in the animal as in the human kind; and ’tis on beauty, strength, swiftness or some other useful or agreeable quality that this passion is always founded.
Hume has already discussed the importance of the bodily component of the amorous passion. The English Philosopher does not hesitate to bring up the filiation between the other animals and the human kind to support his observation—human beings, which are fundamentally animals, are necessarily because materially driven to react to the pleasant and unpleasant sensations of their body, above all rationality (Hume has already demonstrated how human beings act in a profoundly irrational fashion).
How such impulses are, according to Hume, counterbalanced by culturally acquired pleasures (through the richness of the rites and training of the senses) or morally conditioned ones (we naturally tend to prefer what is virtuous), remains unresolved.