ABSTRACT
Reason has been assigned two roles: in its theoretical employment, it is supposed to yield knowledge or, at least, well-founded belief; in its practical employment, it is supposed to regulate passions and in this way govern conduct. David Hume’s first point is that abstract reasoning on relations of ideas can never alone be the cause of an action. He recognizes that abstract reasoning, for example, mathematical reasoning, can have a bearing upon action, as when an engineer uses calculations to guide his constructions, but he claims that these cases always presuppose some antecedently given purpose. Hume also says that reason ought only to be the slave of the passions. Of course, the phrase may simply be a throwaway, saying nothing more than this: since reason is the slave of the passions, it is idle to assign it any other task.
