Deductive-nomological model

The deductive-nomological model (DN model), also known as Hempel's model or Hempel–Oppenheim model or Popper–Hempel model or Covering Law Model, is a formal view of scientifically answering questions asking, "Why...?". DN model poses scientific explanation as a deductive structure—that is, one where truth of its premises entails truth of its conclusion—hinged on accurate prediction or postdiction of the phenomenon to be explained.

Through problems concerning humans' ability to define, discover, and know causality, DN model's initial formulation omitted it, thought to be incidentally approximated by realistic selection of premises that derive the phenomenon of interest from observed, starting conditions plus general laws. Still, DN model formally permitted causally irrelevant factors. Also, derivability from observations and laws sometimes yielded absurd answers.

Upon logical empiricism's 1960s fall, DN model was concluded a flawed or greatly incomplete model of scientific explanation, but remained an idealized version, and rather accurate for modern physics. In the early 1980s, revision to DN model emphasized maximal specificity for relevance of the conditions and axioms stated. Together with Hempel's inductive-statistical model, DN model forms scientific explanation's covering law model, as also termed, from critical angle, subsumption theory.