We speak not strictly and philosophically when we talk of the combat of passion and of reason. Reason is, and ought only to be the slave of the passi… - David Hume

Reason is, and ought only to be the slave of the passions.

Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them.

Custom, then, is the great guide of human life. It is that principle alone which renders our experience useful to us, and makes us expect, for the future, a similar train of events with those which have appeared in the past. Without the influence of custom, we should be entirely ignorant of every matter of fact beyond what is immediately present to the memory and senses. We should never know how to adjust means to ends, or to employ our natural powers in the production of any effect. There would be an end at once of all action, as well as of the chief part of speculation.

There is an universal tendency amongst mankind to conceive all beings like themselves, and to transfer to every object those qualities, with which they are familiarly acquainted, and of which they are intimately conscious. We find human faces in the moon, armies in the clouds; and by a natural propensity, if not corrected by experience and reflection, ascribe malice and good-will to every thing, that hurts or pleases us. Hence the frequency and beauty of the prosopopoeia in poetry, where trees, mountains and streams are personified, and the inanimate parts of nature acquire sentiment and passion. (Section 3, paragraph 2).

The identity that we ascribe to things is only a fictitious one, established by the mind, not a peculiar nature belonging to what we’re talking about.