A logical and epistemic distinction between descriptive statements about what is (facts, states, or events) and normative claims about what ought to be (values, norms, or prescriptions); the distinction specifies that normative conclusions do not follow from purely descriptive premises without at least one normative premise connecting them.

Principle

To move from description to prescription an argument must include an explicit normative premise; absent such a premise, any putative derivation commits a category error.

Demonstration

Illustrative Scenario → Recognition → Action → Consequence: A researcher reports that a city’s air pollution raises respiratory risks (recognition: descriptive claim). Policymakers cannot validly conclude that the city ought to restrict traffic unless they adopt a normative premise (e.g., that reducing preventable health risks ought to be prioritized). The consequence is that policy arguments must make value premises explicit rather than treating facts as self-sufficient reasons for action.

Misapplication

A common error treats empirical findings alone as decisive moral prescriptions (e.g., asserting that because X causes suffering, one therefore ought to enact policy Y) without supplying the intervening normative claim that links the fact to the prescription.

Consequence

Analytical: clarifies that ethical or policy conclusions require normative premises and that debates must expose these premises; methodological: prevents covert value judgments from masquerading as neutral science.

Reversal

When a term’s meaning already encodes normative content (for example, when a definition of a practice includes evaluative criteria), descriptive statements about conformity to that definition can yield normative conclusions internally—i.e., the distinction does not prevent inference where normative content is embedded in terms or axioms.

Boundary

Clearly within: arguments where moral conclusions are drawn from empirical descriptions without added normative premises. Boundary case: policy debates mixing empirical evidence and background value assumptions whose scope is contested. Clearly outside: purely formal logical inferences within an explicitly normative system where both premises are normative.

Semantic Tension

Fact ↔ Value: the practical tension between empirical description and ethical prescription when both are needed for justified action.

Synthesis

The operative lesson is procedural: ethical reasoning must make its normative premises explicit and testable rather than assuming that facts alone determine what ought to be done.