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The Scientific Status of Design Inferences

Original at NAMB Blog

Scientific practice assumes that the universe, in both its origin and function, is a closed system of undirected physical processes. While many scientists reject this assumption as the ultimate truth, they still think that it is essential for science to function as if it were true. This means that they have accepted methodological naturalism as a necessary constraint on their practice as scientists. Methodological naturalism is the doctrine that in order to be scientific, an explanation must be naturalistic, that is, it must only appeal to entities, causes, events, and processes contained within the material universe. Even if we grant that this restriction on permissible explanations has been a fruitful strategy for science, we must still ask whether it is methodologically required by science. Arbitrarily rejecting methodological naturalism may be unwise as an explanatory strategy within science. But perhaps there is a perfectly rigorous  method for ascertaining when such restrictions cannot be applied if a correct explanation for something is to be given. Would such a principled decision, subject to a strict and objective methodology, not also conform to the canons of scientific explanation?

A number of philosophers of science have attempted to give an account of what it means to offer a scientific explanation for a phenomenon. We briefly consider three such accounts: the deductive-nomological model, the  causal-statistical (statistical-relevance) model, and the  pragmatic model.

The deductive-nomological (D-N) model was the earliest model of scientific explanation and has been very influential. It postulates four criteria for scientific explanations:

  1. The explanation must be able to be put in the form of a valid deductive argument, with the thing to be explained as its conclusion.
  2. The explanation must contain at least one general law that is required for the derivation of this conclusion.
  3. The explanation must have empirical content that can be tested.
  4. The premises of the argument constituting the explanation must be true.

Subsequently, it became clear that the D-N model had irremediable shortcomings falling into two categories: (a) there are arguments meeting the criteria of the D-N model that fail to be genuine scientific explanations; and (b) there are genuine scientific explanations that fail to meet the criteria of the D-N model. In short, these four criteria are neither sufficient nor necessary to guarantee that an explanation is scientific. To see this, I offer two standard counterexamples: the man and the pill, and the explanation of paresis.

That the D-N model is insufficient as an account of scientific explanation can be illustrated by this humorous counterexample. A man explains his failure to become pregnant over the last year, despite an amorous relationship with his wife, on the ground that he has regularly consumed her birth control pills. He appeals to the law-like generalization that every man who regularly takes oral contraceptives will not get pregnant. This example conforms to the D-N pattern of explanation. The problem is that his use of birth control is irrelevant because men do not get pregnant. So it is possible to construct valid arguments with true premises in which some fact asserted by the premises is irrelevant to the real explanation of the phenomenon in question.

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Bruce Gordon

Senior Fellow, Center for Science and Culture
Bruce Gordon holds degrees in applied mathematics, piano performance, analytic philosophy, and theology, as well as a doctorate in the history and philosophy of physics from Northwestern University. He is the author of numerous articles in professional journals and edited collections, the editor of two books, and co-author of a third. He has taught at the University of Calgary, Northwestern University, the University of Notre Dame, Baylor University, and The King’s College in New York City. He is currently a professor of the history and philosophy of science at Houston Baptist University, a Senior Fellow of Discovery Institute's Center for Science & Culture, and the President and CEO of