What is Hume’s Law about the relationship between facts and moral duties?

Hume’s Law, named after the Scottish Enlightenment philosopher David Hume, is the principle that moral obligations—statements about what one "ought" to do—cannot be logically derived solely from statements of fact—statements about what "is" the case.12

In his work A Treatise of Human Nature, Hume observed that many writers on morality would begin by making factual observations about human nature or the world, only to suddenly transition to conclusions about moral duties without explaining how such a deduction is possible. Hume argued that this transition is logically illicit, effectively establishing a conceptual gulf between facts and values.23

It is important to note that Hume’s Law is distinct from the principle of "ought implies can," which suggests that an agent has a moral obligation to perform an action only if it is possible for them to do so. By highlighting the gap between "is" and "ought," Hume’s Law serves as a critical tool for identifying instances where values are smuggled into arguments under the guise of factual premises.123