Wednesday, May 27, 2009

Duhem: on the duties of a metaphysician towards science

Our master reveals that our bridge joining science to the rest of the world must work in both directions. Has anyone else noticed a distinct strain of Cardinal Newman in this particular excerpt? I don't recall having read of it in Jaki.
--Dr. Thursday

The Metaphysician Should Know Physical Theory
in order not to make an illegitimate use of it in his speculations

There you have, then, a theoretical physics which is neither the theory of a believer nor that of a nonbeliever, but merely and simply a theory of a physicist; admirably suited to classify the laws studied by the experimenter, it is incapable of opposing any assertion whatever of metaphysics or of religious dogma, and is equally incapable of lending effective support to any such assertion. When the theorist invades the territory of metaphysics or of religious dogma, whether he intends to attack them or wishes to defend them, the weapon he has used so triumphantly in his own domain remains useless and without force in his hands, the logic of positive science which forged this weapon has marked out with precision the frontiers beyond which the temper given it by that logic would be dulled and its cutting power lost.
But does it follow from the fact that sound logic does not confer on physical theory any power to confirm or invalidate a metaphysical proposition that the metaphysician is entitled to distrust the theories of physics? Does it follow that he can pursue the construction of his cosmological system without any concern for the set of mathematical formulas by means of which the physicist succeeds in representing and classifying the set of experimental laws? We do not believe so; we are going to try to show that there is a connection between physical theory and the philosophy of nature; we are going to try to show precisely in what this connection consists.
But first, in order to avoid any misunderstanding, let us make a remark. This question, Does the metaphysician have to take account of the statements of the physicist? applies absolutely only to the theories of physics. The question is not to be applied to the facts of experiment or to experimental laws, for the answer cannot be doubtful; it is clear that the philosophy of nature has to take account of these facts and of these laws.
Indeed, the propositions which state these facts and formulate these laws have an objective import which is not possessed by merely theoretical propositions. The former may then be in agreement or disagreement with the propositions constituting a cosmological system; the author of this system does not have the right either to be indifferent to this agreement, which brings valuable confirmation to his intuitions, or to this disagreement, which condemns his doctrines beyond appeal.
The judgment of this agreement or disagreement is generally easy when the facts considered are facts of everyday experience and when the laws aimed at are the laws of common sense, for it is not necessary to be a professional physicist to grasp what is objective in such facts or in such laws.
On the other hand, this judgment becomes infinitely delicate and thorny when it comes to a scientific fact or scientific law. In fact, the proposition which formulates this fact or law is generally an intimate mixture of experimental observation endowed with ob­jective import and theoretical interpretation, a mere symbol devoid of any objective sense. It will be necessary for the metaphysician to dissociate this mixture in order to obtain as pure as possible the first of the two elements forming it; in that element, indeed, and in that observational element alone, can his system find con­firmation or run into contradiction.

[from P. Duhem, "The Physics of a Believer" reprinted in The Aim and Structure of Physical Theory translated by Philip P. Weiner from the second edition, 1914]

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