iSoul In the beginning is reality

Physics and metaphysics

Physics and Metaphysics” is the English title of an essay by Pierre Duhem in Essays in the History and Philosophy of Science, translated by Roger Ariew and Peter Barker (Indianapolis: Hackett, 1996). It was originally published in 1893 as “Physique et métaphysique.” Below are some excerpts.

We have devoted ourselves above all to delineating the exact role of physical theories, which, in our view, are not more than a means of classifying and coordinating experimental laws. They are not metaphysical explanations that reveal to us the causes of phenomena. p.29

We regard the investigation of the essence of material tings, insofar as they are causes of physical phenomena, as a subdivision of metaphysics. This subdivision, together with the study of living matter, forms cosmology. This division does not correspond exactly to the peripatetic one. The study of the essence of things constitutes metaphysics in peripatetic philosophy. p.30

From the knowledge of phenomena, we can draw some knowledge of the things themselves, because they are the efficient causes of these phenomena and because knowledge of an effect provides us with some information on the substance that causes this effect, without giving us, however, a full and adequate knowledge of that substance. p.31

The knowledge that metaphysics gives us of things is more intimate and deeper than the one provided by physics. It therefore surpasses the latter in excellence. But if metaphysics precedes physics in order of excellence, it comes after physics in the order of logic. p.32

[I]f it is not impossible, it is at least extremely difficult to deduce a new physical truth from well-established metaphysical truths. As for metaphysical systems, they may suggest a proposition in physics, but physics alone can decide if this proposition is correct or incorrect. p.34

This method, which permits the study of physical phenomena and the discovery of the laws that connect them, without recourse to metaphysics, is the experimental method. p.34

The experimental method rests on principles evident in themselves and independent of any metaphysics. p.34

[M]etaphysics aims to give an account of the self-evident foundations on which physics rests. But this study adds nothing to their certainty and to their clarity in the domain of physics. p.35

In classifying a group of experimental laws, physical theory teaches us absolutely nothing about the foundation for these laws and the nature of the phenomena that they govern. p.36

Since none of the propositions, which taken together constitute a physical theory, is a judgment about the nature of things, none of these propositions can ever be in contradiction with a metaphysical truth, which itself is always a judgement on the nature of things. This essential difference between a proposition of theoretical physics and a metaphysical truth shows equally that the one can never be identical to the other. It is therefore absurd to seek among the truth of metaphysics either the confirmation or the refutation of a physical theory, at least to the extent that it remains confined to its proper domain. p.36

The subordination that a theory establishes among various physical laws by classifying them does not oblige us to admit a similar subordination among the metaphysical laws of which the physical laws are the manifestation. p.37

[P]hysical theories and metaphysical truths are independent of one another. p.36

For example, when Archimedes undertakes to write a mathematical theory of floating bodies—the first theory of mathematical physics ever composed—he does not seek to understand what liquids are in themselves and to uncover the metaphysical foundation of their properties. He contents himself with stating a proposition which he names a hypothesis, and with demonstrating that the physical laws of floating bodies can be deduced logically from that hypothesis. p.41

At the end of the sixteenth century and the beginning of the seventeenth, the human mind underwent one of the greatest revolutions ever to turn the world of thought upside down. … Then one saw the disappearance of the ancient barrier separating the study of physical phenomena and their laws from the investigation of causes. Then one saw physical theories taken for metaphysical explanations and metaphysical systems seeking to establish physical theories by deductive means. p.43

The illusion that physical theories attain true causes and ultimate reasons for things penetrates in every sense the writings of Kepler and Galileo. The debates that make up the trial of Galileo would be incomprehensible to anyone who did not see there the struggle between a physicist who wishes his theories to be not only the representation but also the explanation of phenomena, and theologians who maintain the ancient distinction and do not admit that Galileo’s physical and mechanical reasonings might in any way go against their cosmology. p.44

But the person who made the greatest contribution to breaching the barrier between physics and metaphysics is Descartes. p.44

The first proposition in physics that Descartes establishes, by following his method, gives him, he tells us knowledge of the very essence of matter. p.44

This influence of Descartes was extremely general. It was not, however, entirely universal. We have shown … that Pascal did not submit to it without some protest. We have shown above all that Newton never abandoned the tradition of the schools. He always clearly separated scientific theories intended to coordinate physical laws and metaphysical investigations intended to make known the causes of phenomena. He always maintained the logical priority of the first, among which he placed celestial mechanics, over the second. p.46

In the eighteenth and nineteenth centuries, the exact concept of the relations between physics and metaphysics was more and more obscured. p.46

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