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 passions, and can never pretend to any other office than to serve and obey them.

Part 3 Of the will and direct passions, Sect. 3 Of the influencing motives of the will - A Treatise of Human Nature (1739-40) - Of the Passions