Pierre Maurice Marie Duhem (1861 - 1916) was a French physicist, philosopher and historian of science. His most influential work in the philosophy of science came in his classic text, The Aim and Structure of Physical Theory, where he defended several theses, such as a moderate but powerful form of instrumentalism, the underdetermination of theories by evidence (now known as the Quine-Duhem thesis), and confirmation holism.
At the young age of eleven, Duhem entered the Collège Stanislas. By 1882, he had finished his studies with honors in Latin, Greek, science, and mathematics. After Stanislas, Duhem’s father wanted him to study applied science at École Polytechnique so that he could become an engineer. However, his mother, who was a devout Catholic, wanted him to study Latin and Greek at the École Normale Supérieure in fear that a scientific track would lead him away from religion. In 1884, Duhem disappointed both of his parents and enrolled in the École Normale Supérieure to study pure science.
Duhem excelled at the École Normale and succeeded in publishing his first paper in 1884, on electrochemical cells. In fact, Duhem excelled so much that in the same year, he submitted his doctoral thesis, which was on thermodynamic potentials in physics and chemistry. Unfortunately, in the thesis, Duhem argues that Marcellin Berthelot’s criterion for measuring the spontaneity of chemical reactions was incorrect, and that free energy should be used instead. Unfortunately, Berthelot was very influential in France and saw that Duhem’s thesis was rejected. Duhem eventually graduated from the École Normale in 1888, by writing a less controversial thesis in mathematical physics.
Duhem went on to teach at Lille Catholic University until 1893. In fact, Duhem was already teaching there when he earned his doctoral degree; he began in 1887. At Lille, Duhem lectured on hydrodynamics, elastics, and acoustics. He even published three of his lectures in 1891. But in 1893, Duhem had a dispute with the dean and moved to the University of Rennes, which he stayed for only one year due to research equipment limitations. So in 1894, Duhem moved to the University of Bordeaux to become a professor in theoretical physics. Duhem requested a move from Bordeaux to a university in Paris more than once, however; each request was rejected, since Berthelot had been the French minister of education since 1886, and Berthelot still had deep disagreements about thermodynamics with Duhem.
Nevertheless, Duhem kept publishing in physics, developing such innovations as the Gibbs-Duhem Equation in thermodynamics. Three major works of Duhem at Bordeaux were, Thermodynamique et chimie (1902), Recherches sur l'hydrodynamique (1903, 1904), and Recherches sur l'élasticité (1906). In 1900, Duhem’s brilliant research paid off and he was accepted into the world-renowned Academy of Sciences.
Duhem’s fervor for science blossomed into an interest in philosophy of science, which itself fueled an interest in the history of science. In fact, many philosophers of science today consider Duhem to be the first philosopher of science to pay careful attention to the history of science. In fact, many philosophers of science after Duhem, such as Karl Popper [1902-1994], ignored the history of science until Thomas Kuhn (1922-1996) and Imre Lakatos (1922-1974) revived the importance of the history of science in the philosophy of science in the mid-1900s.
A few of Duhem’s major works in the philosophy and history of science were L'évolution de la mécanique (1902), Les origines de la statique (1903), and La Théorie physique: son objet et sa structure (1906). However, Duhem’s publications were vast and his drive to publish was astonishing. In fact, due to his prowess in the history and philosophy of science, Duhem was eventually offered a professorship in Paris as a historian of science. However, he rejected the position because it was not in physics. Duhem later died in 1916.
Duhem had at least three books in philosophy of science, but his most prominent one was The Aim and Structure of Physical Theory, which was published in 1906, and translated into English in 1954, with a notable foreword by the Nobel laureate Louis de Broglie (1892-1987). In this book, Duhem posited three major theses: Instrumentalism, the underdetermination of theories by evidence, and confirmation holism.
Duhem’s philosophy of science rests on a firm distinction between physics and metaphysics. Duhem believed that contrary to many physicists before him, physics was not subordinate to metaphysics. But rather, physics could be conducted entirely independently of one’s metaphysical beliefs, and, moreover, physics should be conducted in this way because the worth of a physical theory lies in its non-metaphysical features.
Duhem proposed that a physical theory should consist of an abstract list of axioms, whose deductions predict the phenomenal laws in a particular domain of physics with as much completeness, precision, and simplicity as possible. In Duhem’s words:
A physical theory is not an explanation; it is a system of mathematical propositions whose aim is to represent as simply, as completely, and as exactly as possible a whole group of experimental laws (Duhem 1954, 19).
Duhem’s picture is that physicists should observe a physical phenomenon, synthesize a law for the phenomenon, and then propose a simple, complete, and precise mathematical hypothesis that together with reasonable background assumptions implies the phenomenological law. This method had been known as the hypothetico-deductive approach since Christiaan Huygens [1629-1695], but Duhem’s innovation was suggesting that the method did not require any metaphysical commitments.
For example, Isaac Newton (1642-1727) had a difficult time promoting his gravitational theory among his contemporaries because it posited an action-at-a-distant force, which conflicted with the popular seventeenth century view that all physical causes operate through contact interaction, like billiard balls. Nevertheless, Duhem would say that the value of Newton’s gravitational theory lies in its ability to predict Kepler’s laws of planetary motion from the law of gravity and certain background assumptions, and that progress in physics should not be held up just because the theory violates metaphysical dogma.
Since Duhem’s picture of physical theories eliminated ontological commitments in physical theory, his view on physical theory was anti-realist. Anti-realists believe that scientific theories do not give knowledge about the external world. Rather, according to Duhem, physical theories merely save phenomena in economical mathematical formulas. In fact, Duhem wrote another book in 1908, on the idea of physical theory from Plato to Galileo entitled To Save the Phenomena. This particular view on scientific theories is known as instrumentalism, since scientific theories are seen as not just anti-realist, but as mere instruments for human use.
Duhem was not the first to view physical theories as instrumentalist. Ernst Mach (1838-1916), a renowned Austrian-Czech physicist and philosopher, valued physical theories for their “economy of thought” and Duhem often referenced Mach in his writings. Nevertheless, it is not entirely fair to present Duhem as a simple instrumentalist. Duhem thought that some sub-fields of physics had attained genuine knowledge, such as acoustics. Duhem also struggled with the idea that mere instruments can predict future phenomena (e.g. how Newton’s law of gravity can predict the periodicity of Halley’s comet). Duhem was also careful to circumscribe his views to physical theory and did not carelessly extend his views on physical theory to chemical and biological theory. So, some philosophers categorize Duhem’s views somewhere between instrumentalism and realism.
Despite the nuances in Duhem’s view, he was certainly an instrumentalist about invisible physical entities such as atoms and subatomic particles, a point that de Broglie chastised him for in his 1954 foreword. Thus, Duhem was certainly an entity anti-realist, which is a philosopher who believes that the entities posited by science are mere fictions. In fact, contemporary entity realists, such as Nancy Cartwright (1983) and Ian Hacking (1984) begin the defense of their views by addressing Duhem’s skepticism about the reality of physical entities. Duhem’s entity anti-realism stems from his insistence on the axiomatic method in physical theorizing and his distaste for geometrical representations of unobservable physical states and entities.
For better or worse, the logical positivists used Duhem’s instrumentalism as a philosophical grounding for promoting their program. Logical positivism was a school of philosophers of science, closely associated with the Vienna Circle, who believed that metaphysical statements were unverifiable in principle and thus meaningless. Thus, logical positivists drew a clear line between science and mathematics on one hand and metaphysics and religion on the other. Notable members of the Vienna Circle were Rudolf Carnap (1891-1970), Hans Reichenbach (1891-1953), and Carl Gustav Hempel (1905-1997). Through Duhem’s philosophical views, logical positivists were able to extend instrumentalism to the then developing theory of quantum mechanics. This led to the development of the Copenhagen interpretation of quantum mechanics by Niels Bohr (1885-1962) and Werner Heisenberg (1901-1976), which is still the most widely acknowledged interpretation of quantum mechanics to this day.
Perhaps the most important contribution Duhem made to the philosophy of science was his thesis that physical theories are underdetermined by any evidence that one could produce. Duhem’s thesis can be stated in the following precise way.
In hypothetico-deductive (or abductive) reasoning, physicists propose a hypothesis and then deduce consequences from the hypothesis that can be observed. If the consequences are observed, then those observations are considered to be evidence for the truth of the hypothesis. However, since this sort of reasoning is deductively invalid, no amount of evidence can prove that a hypothesis is true.
Since physicists already knew that the hypothetico-deductive approach is deductively invalid, physicists depended on the deductive validity of falsification. Falsification is continuous with the hypothetico-deductive approach since it licenses the rejection of a hypothesis if the opposite of one of its observable consequences turns out to be observed. In this case, physicists often say that the observation of the opposite of the consequence serves as counterevidence against the truth of the hypothesis, and often speak of such an observation being a “crucial experiment” against a hypothesis.
However, Duhem’s thesis is that just in order to derive observable consequences from a physical hypothesis, physicists need to make background assumptions about the experimental setup, instruments, how the phenomena should be idealized, and so forth. Thus when a consequence is not observed, this is not evidence that the hypothesis is false, it is only evidence that there is a falsity somewhere in the whole set of background assumptions in addition to the hypothesis. Hence, any physical theory is underdetermined by any evidence one could provide in support or against the theory.
Duhem’s underdetermination thesis was expanded by Willard van Orman Quine (1908-2000) to include mathematical and metaphysical propositions in the list of background assumptions that could be rejected in the face of conflicting observations. Philosophers call Duhem’s (1954) and Quine’s (1951) theses combined the Quine-Duhem thesis, and it is recognized as one of the most profound theses in the philosophy of science. Thus when a physicist observes phenomena that conflict with a hypothesis, he can reject the hypotheses, an observational assumption, a theoretical assumption, a mathematical or logical assumption, or even a metaphysical assumption. This last point brings us to Duhem’s final major contribution to philosophy of science: Confirmation holism.
Due to the pervasiveness of the underdetermination of physical theory by evidence and the vastness of background assumptions needed for any modern physical experiment, Duhem postulated that the whole of physics was brought into question when a physical observation conflicted with a physical theory. Thus it is inappropriate to view physical theories in isolation. There is no such thing as a physical theory being right or wrong. The most a physicist can say about a physical theory is that it coheres with the rest of physics or it does not. Unsurprisingly, Quine (1970), along with his student Joseph S. Ullian, improved on this idea as well to include all background beliefs, including mathematical and logical beliefs, as revisable in what he called “the web of beliefs.”
The reason Duhem was driven to such a holistic view of physical theory was because he thought it was in principle impossible to know when one has isolated the false assumption in the host of background assumptions a physicist needs to conduct an experiment.
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