The Aim and Structure of Physical Theory

by Pierre Duhem, Philip P Wiener (Translation), Jules Vuillemin (Introduction)

This classic work in the philosophy of physical science is an incisive and readable account of the scientific method. Pierre Duhem was one of the great figures in French science, a devoted teacher, and a distinguished scholar of the history and philosophy of science. This book represents his most mature thought on a wide range of topics.

Genres: Philosophy, Science, Physics, Nonfiction

513 pages, Kindle Edition

First published January 1, 1906

About the author

Pierre Maurice Marie Duhem (French: [pjɛʁ moʁis maʁi dy.ɛm] was a French physicist, mathematician, historian and philosopher of science. He is best known for his work on chemical thermodynamics, for his philosophical writings on the indeterminacy of experimental criteria, and for his historical research into the science of the European Middle Ages. As a scientist, Duhem also contributed to hydrodynamics and to the theory of elasticity.

Duhem's views on the philosophy of science are explicated in his 1906 work The Aim and Structure of Physical Theory. In this work, he opposed Newton's statement that the Principia's law of universal mutual gravitation was deduced from 'phenomena', including Kepler's second and third laws. Newton's claims in this regard had already been attacked by critical proof-analyses of the German logician Leibniz and then most famously by Immanuel Kant, following Hume's logical critique of induction. But the novelty of Duhem's work was his proposal that Newton's theory of universal mutual gravity flatly contradicted Kepler's Laws of planetary motion because the interplanetary mutual gravitational perturbations caused deviations from Keplerian orbits. Since no proposition can be validly logically deduced from any it contradicts, according to Duhem, Newton must not have logically deduced his law of gravitation directly from Kepler's Laws.

Duhem's name is given to the under-determination or Duhem–Quine thesis, which holds that for any given set of observations there is an innumerable large number of explanations. It is, in essence, the same as Hume's critique of induction: all three variants point to the fact that empirical evidence cannot force the choice of a theory or its revision. Possible alternatives to induction are Duhem's instrumentalism and Popper's thesis that we learn from falsification.

As popular as the Duhem–Quine thesis may be in the philosophy of science, in reality, Pierre Duhem and Willard Van Orman Quine stated very different theses. Pierre Duhem believed that experimental theory in physics is fundamentally different from fields like physiology and certain branches of chemistry. Also, Duhem's conception of the theoretical group has its limits, since not all concepts are connected to each other logically. He did not include at all a priori disciplines such as logic and mathematics within these theoretical groups in physics which can be tested experimentally. Quine, on the other hand, conceived this theoretical group as a unit of a whole human knowledge. To Quine, even mathematics and logic must be revised in light of recalcitrant experience, a thesis that Duhem never held.

A quote of Duhem on physics:

A theory of physics is not an explanation. It is a system of mathematical propositions, deduced from a small number of principles, which have for their aim to represent as simply, as completely and as exactly as possible, a group of experimental laws.

Reviews

[Airam · Rating 4 out of 5]

I was enthralled with Sauver les apparences : sozein ta phainomena and immediately took up this book afterwards. It's a pleasure to be engrossed in Duhem's encyclopedic knowledge and follow his original lines of thinking and brilliant associations. Rivers of ink could be - and have been - writen about the ways this book has influenced physicists and philosophers in the past century. Now, this is not what the whole book is about and a lot more is beautifully discussed, but for me it was particularly interesting to find out the origins of the underdetermination debate, which since then have blown out of proportion.
The underdetermination arguments bear on the relation between empirical data and the theories we associate to them. The central idea is that the data available at a given time may be insufficient to determine what beliefs can be held about them, since the data can in principle be explained by many mutually incompatible theories.
Duhem set ablaze the discussion about underdetermination in science when he argued that experiments in physics can neither confirm nor falsify individual laws or hypotheses but only groups of them. This thesis (not exclusively applied to physics) is called confirmational holism. The consequence is that, when predictions fail, we have no way of knowing if the fault lies with our hypothesis or in any of the other beliefs and hypotheses we used to make our prediction. If the predicted phenomenon is produced through experiment, it is not derived from the challenged proposition alone but from a set of theories. Conversely, if the predicted phenomenon is not produced, the only thing that tells us is that there is a problem with at least one of the propositions we used, not necessarily the challenged one. This we call holist underdetermination (once again, not exclusive of physics).
Duhem further argues that an experimentum crucis is impossible, i.e., that there can be no irrefutable procedure for demonstrating the truth of one of the two hypotheses and solve the impasse. An experimental result predicted differently by two competing theories does not confirm one and refute the other beyond doubt, because we can never be sure that other consequences of the theory will not be contradicted by experiment, or that a future theory will not be able to interpret the facts just as well.
The example given by Duhem here is remarkable not only for epitomizing this thesis but also for revealing great penetration and instinct before the unknown. Consider the 19th century debate between physicists concerning the nature of light. There were those who argued light consisted in projectiles hurled with extreme speed and those who argued it consisted of vibrations whose waves are propagated within an ether. These are called the emission theory of light and the wave theory of light, respectively. The physicist Léon Foucault designed in 1849 an experiment to test the two theories’ competing claims about the speed of transmission of light in different media: the particle theory predicted light would travel faster in water than in air, while the wave theory predicted the opposite. Foucault’s apparatus of a rotating mirror demonstrated that the speed of propagation of light in water is less than the speed of propagation of light in a vacuum. In 1905, when La théorie physique was being written, Foucault’s apparatus was thought to have given a crucial proof in favour of the wave theory of light, but Duhem argued that the result of the experiment could be interpreted by Fresnel’s theory and that while it contradicts Newton’s corpuscular theory, it is possible that another corpuscular theory will come along that can interpret it. As Duhem put it, “it is not between two hypotheses, the emission and wave hypotheses, that Foucault's experiment judges trenchantly; it decides rather between two sets of theories each of which has to be taken as a whole, i.e., between two entire systems, Newton's optics and Huygens' optics.” In other words, Foucault's experiment doesn’t necessarily refute the theory of emission, but proves only that Newton’s whole theory from which we deduce the relation between the index of refraction and the velocity of light in various media is wrong. Whether the error is in the fundamental hypothesis that light consists in projectiles hurled with great speed by luminous bodies or in some other assumption concerning the actions experienced by light corpuscles due to the media in which they move, we do not know. In retrospect, the light example was almost prescient, for the photon has since then been postulated and proven to exist, and it is the base of our current theories of light, though the wave-particle debate lives on.
Duhem contrasts mathematical and physical procedures: whereas between two contradictory theorems of geometry, if one is false, the other is necessarily true, experimental contradiction does not make one physical theory necessarily true and the other false. "In sum, the physicist can never subject an isolated hypothesis to experimental test, but only a whole group of hypotheses; when the experiment is in disagreement with his predictions, what he learns is that at least one of the hypotheses constituting this group is unacceptable and ought to be modified; but the experiment does not designate which one should be changed."
Duhem’s problems of scientific underdetermination challenged the confirmation of theories only in the realm of physics, as he himself argued, but, half a century later, in Two Dogmas of Empiricism, Quine advocated that such challenges applied to the confirmation of all types of scientific theories. In fact, Quine extended the challenge to all knowledge claims whatsoever. Since then, other philosophers have systematized fundamentally different lines of thinking within underdetermination and worked out from them multiple theses. There is, for instance, an established division between holist and contrastive forms of underdetermination, and within them arise stronger or weaker varieties, with different consequences for scientific inquiry.

[Etienne OMNES · Rating 5 out of 5]

La théorie physique: son objet, sa structure est un traité de philosophie des sciences écrit par Pierre Duhem, grand scientifique du début 20e siècle, ainsi que philosophe et historien des sciences. Ce livre expose la nature et la structure d'une théorie scientifique. Il défend notamment l'idée que les théories ne sont pas une *explication* de la réalité (un récit de ce qu'est vraiment la nature) mais une simple classification intellectuelle destinée à relier entre elles toutes les lois expérimentales.

La partie 1 décrit ce qu'est une loi physique, et il y détaille avec beaucoup de clarté et d'équilibre la vraie nature des lois physiques: des constructions intellectuelles et non des explications de la réalité.
La partie 2 décrit la structure et comment on doit construire les théories physiques: il y aborde notamment l'impossibilité de faire des expériences sans bagage théorique préalable, l'importance de distinguer les lois physiques des lois de bon sens, et comment bien choisir ses hypothèses etc.

Ne ratez pas également l'appendice "la physique du croyant" où Pierre Duhem aborde la question "qu'est ce que la Science a à voir avec Jérusalem?" ou la relation entre métaphysique/religion et physique. Il affirme que les deux ont des domaines différents, et que la réalité appartient à la religion.

Un traité très éclairant, très clair et bien argumenté. La deuxième partie est un peu plus dense que la première, mais le tout reste accessible. Tout chrétien avec une vocation scientifique devrait le lire.

[Alan · Rating 5 out of 5]

Duhem gives a very insightful summary of how modern physics operates. It has reaffirmed my view, molded by doing physics myself, of how physics should work and what its aims are. Every physicist and philosopher interested in reconciling true philosophy with modern physics should read this book. It really opened me up to what "saving the phenomena" means and to what modern physics' strengths and weaknesses are.

This quote well-summarizes his position on how metaphysics relates to physics:

Now these two questions -- Does there exist a material reality distinct from sensible appearances? and What is the nature of reality? -- do not have their source in experimental method, which is acquainted only with sensible appearances and can discover nothing beyond them. The resolution of these questions transcends the methods used by physics; it is the object of metaphysics.
Therefore, if the aim of physical theories is to explain experimental laws, theoretical physics is not an autonomous science; it is subordinate to metaphysics.

He argues it is autonomous, though. His engineer friend Eugène Vicaire criticized Duhem's postivistic conception of the relation of physics to metaphysics as "the poison of skepticism." Vicaire wrote:

It is not true that when constructing its theories, positive science has as its object simply to classify experimental laws; its proper object is the discovery of causes. To deny this is to maintain a suspect doctrine of positivism, and one capable of leading to skepticism. That doctrine, condemned by the whole tradition of great physicists, is dangerous, for it destroys scientific activity.

Pages 207-209 of William A. Wallace's excellent The Modeling of Nature: Philosophy of Science and Philosophy of Nature in Synthesis contain a good critique of Duhem's philosophy of science.

Duhem's views on metaphysics' relation to modern physics are contradictory to me. First he says in this book that physical theory is not subordinate to metaphysics nor can metaphysics edify it, then later he says that although physical hypotheses develop within a physicist, metaphysics offers a guide to what he should consider fundamental elements of it, as though modern physics is indeed subordinate to metaphysics. The whole criticism of Duhem rests on his "fideist" separation of physical theory from metaphysics, as this excellent biography of Duhem attests (esp. pgs. 203-206).

Also, his lengthy discussion of the historical development of the formulation of the 1/r² law of gravitation was enlightening. It proved the necessity of teaching physics with the so-called historical method, as Duhem writes:

The legitimate, sure and fruitful method of preparing a student to receive a physical hypothesis is the historical method. To retrace the transformations through which the empirical matter accrued while the theoretical form was first sketched; to describe the long collaboration by means of which common sense and deductive logic analyzed this matter and modeled that form until one was exactly adapted to the other: that is the best way, surely even the only way, to give to those studying physics a correct and clear view of the very complex and living organization of this science.

In summary, as interesting as that book is—and he does an excellent job explaining how physics operates through his historical examples—I still think he has an unclear (at least it seems unclear to me) notion of what exactly the role of metaphysics is in relation to modern physics. At the beginning of the book he seems to think metaphysics plays no role (he gives the historical example of Fresnel on how optics effectively "transcended" the metaphysics that inspired the theories); then he says maybe certain metaphysics can play a role; then toward the end he says metaphysics plays the role in determining what elements of physical theories one should consider fundamental. {Perhaps he is merely distinguishing the "via inventionis" ("way of discovery") from the "via resolutionis" ("way of resolution"); in the former metaphysics plays no role but in the latter it does, or vice versa?} Still, it is a very fascinating book; his attempt to show the relation between modern physics and metaphysics is noble; but his philosophy of physics (that physical theories are just equations and that all modern physics does is classify) seems to discount physics's explanatory power. Duhem has been infected with a small dose of skepticism.