Explanans

Explanans is a term used in philosophy of science to denote the part of an explanation that provides the grounds or reasons for a phenomenon. It is contrasted with explanandum, the phenomenon or fact that requires explanation. Together, the explanans and explanandum constitute an explanatory relation: the explanans allegedly makes the explanandum intelligible.

Typically, the explanans consists of the statements that supply the causal, lawlike, or statistical backing for the explanation. This can include general laws or well-supported generalizations, specific initial or boundary conditions, and any relevant causal or mathematical relationships. The strength of an explanation is often judged by the relevance, generality, and predictive power of the explanans.

The concept is closely associated with the deductive-nomological (DN) model proposed by Carl Hempel and Paul Oppenheim, where an explanation is a deductive argument in which the explanans, given the premises (including laws and initial conditions), entails the explanandum. In this view, the explanans functions as the logical engine that produces the explanandum.

Examples illustrate the idea: explaining why a tennis ball lands in the court may involve the laws of projectile motion and initial conditions (explanans) that entail the landing position (explanandum); explaining why the sky is blue involves Rayleigh scattering and the solar spectrum as the explanans.

Philosophical work also debates alternatives to the DN model, recognizing that explanations can be causal, statistical, or unifying beyond strict deductive-nomological form. Regardless of the model, explanans refers to the component of explanation that grounds the phenomenon being explained.