Nomological-Deductive Explanations N-DEs

N-DEs are the standard form of explanation in science and take the following form. Given a set of facts (e.g., initial and boundary conditions) and a set of laws (be they causes, processes, or outcomes see Bock 1993), both of which form the explanatory sentence, or explanans, a particular conclusion, or explanandum, follows (Hempel and Oppenheim 1948 Hempel 1965 335-338). N-DEs answer the question, how has a particular phenomenon [explanandum] occurred N-DEs apply to universal (nonlimited sets of phenomena) and 

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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. 

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