Know your scholars: Pierre Duhem

Pierre Duhem (1861-1916) was a French physicist and one of the most important historians and philosophers of science at the beginning of the twentieth century. While he is best known for his indeterminacy thesis and his conjectures about the history of the Middle Ages, Duhem also made notable contributions to thermodynamics, elasticity, and hydrodynamics.

While researching the origins of statics, Duhem uncovered treatises written by medieval philosophers like John Buridan, Nicole Oresme and Roger Bacon. The sophistication of their work shocked him. Duhem consequently rejected the widely held view that the Middle Ages was a dark age devoid of learning.

He also came to believe that these medieval scholars laid the foundation for much of modern science and even anticipated many of the discoveries of Copernicus and Galileo. Since he published these ideas, historians of science and of the Middle Ages have largely vindicated Duhem's ideas about the worth of medieval scholarship.

As monumental as his contributions were to history, Duhem played an equally important role in the development of modern philosophy of science. In his opus, The Aim and Structure of Physical Theory, Duhem provided scholars with a feast of interesting ideas which are still widely discussed and debated.

One of the the most thought provoking of these ideas was Duhem's challenge to classical reductionism. If you are unfamiliar with classical reductionism, it is the thesis that specific laws of science will be shown to be logical extensions of more general laws. In this sense, they are deduced like a sound conclusion in a mathematics or logic problem. For example, Isaac Newton claimed that he deduced his law of universal mutual gravitation from Johannes Kepler's laws of planetary motion. This led Newton to believe that Kepler's laws are nothing more than his own more general principle expressing itself in a certain situation. 

Duhem challenged this assessment by arguing that Newton's law contradicted Kepler's. More specifically, he explained that the interplanetary mutual gravitational perturbations caused deviations from Keplerian orbits (in layman's terms: Kepler's planetary orbits are slightly thrown off by other forces acting on them. This can include tugs from other planets or resistance from an atmosphere. Newton came up with the calculus and physics that demonstrates this). Since deductive logic requires that we cannot derive a false conclusion from true premises (or if we are trying to show that Newton's law is deduced from Kepler's, a conclusion from contradictory premises), Duhem thought that Kepler's laws could not be deduced from Newton's.

His biggest challenge to reductionism, however, was the Duhem Thesis. This thesis argued that reductionism is not possible because of the methodological differences between physics and the other sciences. Given that physics is the only field in which a single hypothesis can be isolated and tested, Duhem argued, there is no way the other sciences can be reduced to it. They are simply too different in their techniques and experiments to be subsumed into physics. This thesis is often mistaken to be the same as a similar one proposed by the American philosopher, Willard van Orman Quine (1908-2000).

Despite the popularity of this, the two men had very different views on science. Quine's thesis argues that one must make assumptions about a number of ideas to test a hypothesis. For example, one must assume things the laws of optics and planetary motion to test their hypothesis about the rings of Saturn. This means that no hypothesis, not even those of physics, can be done in isolation. Quine is also a realist who accepted the existence of scientific objects like atoms. Duhem, on the other hand, assumed that unobservable things like atoms were "useful fictions" used to make predictions.

While Pierre Duhem's legacy may today be partially (or largely) forgotten, he was a key figure in the history and philosophy of science. His work highly influenced a number of scholars in both history and philosophy, including the great Thomas Kuhn (1922-96).