What role did reason play in David Hume’s theory of human action?

In David Hume’s theory of human action, reason plays a strictly limited, instrumental role. Hume famously characterized reason as "the slave of the passions," arguing that it is incapable of initiating action on its own.12

According to Hume, the function of reason is to discover truths about the world and to determine the most effective means to achieve specific ends. However, reason cannot determine what those ends should be; it cannot generate the desires, wants, or feelings that actually motivate human behavior. Because morality is essentially practical—meaning it must incline an individual to act—Hume concluded that moral judgments cannot be based on reason alone, as reason is inert and cannot move one to action without a prior desire.12

Ultimately, for Hume, preferences and actions are driven by sentiments and passions rather than rational deliberation. He asserted that it is not contrary to reason to prefer the most trivial outcome over the most significant one, provided that the preference is rooted in one's own desires or feelings.12