Deductive-nomological
From Biocrawler, the free encyclopedia.
The D-N model is a formalisation of natural language scientific explanations.
Background
The D-N model is taught implicitly in schools, and constitutes the pre-reflective conception of science which many non-experts hold. The D-N model 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. It was devised as a prescriptive form for scientific explanations, but due to the way the model exchews any account of causality, modelling or simplification it is no longer accepted as dogma.
Formalisation
The model sets the following form for scientific explanation that is similar to that of a sum or calculation:
- [S] (Explanans)
- [P] (Explanandum)
Contained within [P] are sets of statements which describe the phenomenon to be explained. They are given the name ‘explanandum’ and provide a description of the phenomena.
Contained within [S] are a number of statements that ‘explain’ the statements in [P]. Amongst the statements in [S] must be at least one statement of a very specific type.
There must be one statement which is in general ‘law-like’ or general. Some statement of the form: All Fs are Gs.
The final consideration of form pertains to the relation between the explanans [S] and the explanandum [P]. This relation is one of logical entailment. Which is to say given the set of explanans statements [S], it must be possible to deduce the explanandum [P].
