The "Is-Ought" gap, also known as Hume's Law, is a critical concept in applied ethics and philosophy, particularly in discussions surrounding moral reasoning and the relationship between descriptive statements (what is) and prescriptive statements (what ought to be). The term originates from the Scottish philosopher David Hume’s work, particularly in his "A Treatise of Human Nature" (1739–40), where he observed that there seems to be a logical gap between statements about facts or states of affairs (what is) and normative or evaluative statements about what should be the case (what ought to be). Hume's insight fundamentally challenges the straightforward derivation of moral conclusions from empirical premises.

The core of the "Is-Ought" gap lies in the observation that facts alone do not logically lead to moral conclusions. For example, one might state that "humans have historically engaged in war" (an is statement, describing a fact about human behavior), but this does not directly imply that war is morally acceptable or desirable (an ought statement, prescribing a