Poincaré, Jules Henri (1854–1912)

Although primarily a mathematician, Henri Poincaré wrote and lectured extensively on astronomy, theoretical physics, philosophy of science and philosophy of mathematics at the turn of the century. In philosophy, Poincaré is famous for the conventionalist thesis that we may choose either Euclidean or non-Euclidean geometry in physics, claiming that space is neither Euclidean nor non-Euclidean and that geometry is neither true nor false. However, Poincaré’s conventionalism was not global, as some have claimed. Poincaré held that only geometry and perhaps a few principles of mechanics are conventional, and argued that science does discover truth, despite a conventional element. Poincaré followed new developments in mathematics and physics closely and was involved in discussion of the foundations of mathematics and in the development of the theory of relativity. He was an important transitional figure in both of these areas, sometimes seeming ahead of his time and sometimes seeming very traditional. Perhaps because of the breadth of his views or because of the way in which philosophers focused on issues or small pieces of his work rather than on accurate history, interpretations of Poincaré vary greatly. Frequently cited by the logical positivists as a precursor, and widely discussed in the philosophy of science and the philosophy of mathematics, Poincaré’s writings have had a strong impact on English-language philosophy.