Hume denies that reason plays a determining role in motivating or discouraging behavior. Instead, he believes that the determining factor in human behavior is passion. As proof, he asks us to evaluate human actions according to the criterion of “instrumentalism”—that is, whether an action serves the agent’s purpose.

Generally, we see that they do not and that human beings tend to act out of some other motivation than their best interest. Based on these arguments, Hume concludes that reason alone cannot motivate anyone to act. Rather, reason helps us arrive at judgments, but our own desires motivate us to act on or ignore those judgments. Therefore, reason does not form the basis of morality—it plays the role of an advisor rather than that of a decision-maker. Likewise, immorality is immoral not because it violates reason but because it is displeasing to us. This argument angered English clergy and other religious philosophers who believed that God gave humans reason to use as a tool to discover and understand moral principles. By removing reason from its throne, Hume denied God’s role as the source of morality.