) model is a formalized view of scientific
explanation in natural language
. It characterizes scientific explanations primarily as deductive arguments with at least one natural law statement among its premises. "Nomological" comes from the Greek word "νόμος
" (nomos), i.e., "law."
The D-N model is known by many names, including the covering law model
, the subsumption theory
, Hempel's model
, the Hempel-Oppenheim model
, and the Popper-Hempel model
of explanation (Niiniluoto, 1995). Its introduction in the philosophical literature is part of a broad general discussion about the nature of scientific explanation (i.e., what it is, what it should be, etc.).
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 formalized by Carl Hempel and Paul Oppenheim in their article Studies in the Logic of Explanation (1948). A sketch of it can be found in Karl Popper's Logic of Scientific Discovery (1959).
The model offers the following account of scientific explanation
, where an explanation is set out as a formalized argument:
- Let p be the explanandum - the statement that describes the phenomenon or phenomena to be explained.
- Let s1. . . sn be the explanans - the statements that "explain" the statement P.
In the D-N model, at least one of the statements si must be a "law-like" statement--a problematic concept, but initially thought to be captured by universal affirmatives, i.e., statements of the form "all X are Y." The explanans must be appropriately testable or observable--they must have "empirical content." If the premises are all true and if the argument is deductively valid, then the following constitutes a correct deductive-nomological explanation of p:
s1. . . sn, therefore, p
As a very simple illustration, consider the following: we observe that a piece of chalk falls when released. Why does the chalk fall? A D-N explanation might look like this (without attending to all subtleties in the precisely correct statement of the premises and conclusion):
- Massive objects attract each other with a force proportional to their masses and inversely proportional to the square of their distance apart.
- The chalk and Earth are massive objects.
- Holding the chalk overcomes the force of attraction between it and Earth
- Therefore, the chalk falls when released
The model is positivist in tone and implication, devised as a prescriptive form for scientific explanations. Due to the way that the model eschews any account of causality, scientific modelling, or simplification--and the general rejection of logical positivism--it is no longer accepted as dogma.
References and further reading
- Hempel, Carl G., and Oppenheim, Paul (1948). "Studies in the Logic of Explanation". Philosophy of Science 1948:15, 135-75; reproduced in Hempel, Carl G. (1965). Aspects of Scientific Explanation. New York: Free Press.
- Mayes, Randolph G. (2006). "Theories of Explanation". The Internet Encyclopedia of Philosophy, Fieser & Dowdwn (eds.), http://www.iep.utm.edu/e/explanat.htm
- Niiniluoto, Ilkka (1995). "Covering Law Model". The Cambridge Dictionary of Philosophy, Robert Audi (ed.), New York: Cambridge University Press.
- Popper, Karl. (1959). The Logic of Scientific Discovery. London: Hutchinson.
- Salmon, Wesley (1990) Four Decades of Scientific Explanation, University of Minnesota Press.
- Woodward, James. (2003). "Scientific Explanation". The Stanford Encyclopedia of Philosophy, Edward N. Zalta (ed.), http://plato.stanford.edu/entries/scientific-explanation/
Types of inference