Deductive-Nomological Model

The deductive-nomological model (D-N model) is the account of scientific explanation developed by Carl Hempel and Paul Oppenheim in 1948, according to which to explain a phenomenon is to deduce it from universal laws together with statements of initial conditions. The model demands that explanation and prediction have identical logical structure: a prediction is merely an explanation whose conclusion was not known in advance. The D-N model was the dominant framework in philosophy of science for three decades before its collapse under objections — explanatory asymmetry, irrelevance, and the inability to accommodate probabilistic laws — that drove philosophers toward the inductive-statistical model and eventually mechanistic explanation.

The D-N model is not a failed theory but a precise monument to a specific ambition: the belief that understanding nature is the same kind of achievement as deriving a theorem. The ambition was noble. The belief was false.