Nomological-deductive explanations

Nomological-Deductive Explanations (N-DEs) Historical-Narrative Explanations (H-NEs)... 

Two different, but interrelated systems of explanations exist in biology, which are (a) the dichotomy of N-DEs versus H-NEs, and (b) the dichotomy of functional explanations versus evolutionary explanations. The latter system stems from the division of biology into the major areas of functional and evolutionary biology (Mayr, 1982). These two systems of explanations in biology do not have a simple relationship to one another. All functional explanations are N-DEs and all H-NEs are evolutionary, but evolutionary explanations can be either N-DEs or H-NEs. Hence it is essential not only to characterize carefully the properties of N-DEs and H-NEs, but to show which parts of biology, and especially of evolutionary biology, are nomological-deductive and which are historical narrative. 

More fundamentally, reductionism as a thesis about inter-theoretical explanation was undermined by the eclipse of the Deductive-Nomological model. Once philosophers of science began to doubt whether deduction from laws was sufficient or necessary for explanation, the conclusion that inter-theoretical explanation need take the form of reduction was weakened. 

According to a classification going back to Coffa (1974) there are two major families of models of scientific explanation epistemic and ontic models. The representative of epistemic model is the Hempelian Deductive-Nomological, abbreviated DN-model and the main representative of ontic model is the causal model of explanation. I discuss each in the following. 

It is quite obvious that this could hardly be considered a scientific law. Thus, there is no way to describe the process of deriving output values as a nomic deduction or as an argument referring to a certain law or a number of laws. And this is exactly what the deductive nomological model of explanation requires. 

Hence the attempt to subsume molecular mechanics under the DN-model of scientific explanation fails. It fails twice First, the stun of the force-field potentials used in molecular mechanics calculations does not have the status of a proper scientific law and the derivation of the strain energy of a molecule by molecular mechanics is not nomological. Second, the conformational search required to find stable conformations is stochastic and not deductive. 

A second question a philosopher might raise is what is the import of equation 25 Can it be used in a deductive nomological explanation of the existence of equilibrium Are its predictions rehable Can it be used to test the validity of a theory which now includes thermodynamic requirements for equilibrium and the ideal gas law ... 

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