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Deductive-nomological

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The deductive-nomological, or D-N model is a formalisation of scientific explanations in natural language.

[edit] Background

The D-N model is taught implicitly in schools, and approximates our pre-theoretical conception of science, which many non-experts hold. It was initially formalised by Carl Hempel, although a sketch of it can be found in Popper's Logic of Scientific Discovery.

The model is positivist in tone and implication, devised as a prescriptive form for scientific explanations, but due to the way that the model eschews any account of causality, scientific modelling, or simplification, it is no longer accepted as dogma.

[edit] Formalisation

The model sets the following form for scientific explanation, similar to that of a sum or calculation:

  • P (Explanandum) - statements that describe the phenomenon to be explained and provide a description of the phenomena
  • S (Explanans) - statements that "explain" the statements in P, at least one of which is a specific statement, and at least one general, "law-like" statement (ex., "all Xs are Ys")

The final consideration of form pertains to the relation between the explanans (S) and the explanandum (P). This relation is one of logical entailment - given the set of explanans statements, it must be possible to deduce the explanandum.

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