Pierre de Fermat
1601–1665, Beaumont-de-Lomagne, France, Castres, France
French magistrate and 'prince of amateurs' who founded modern number theory, conjectured what became known as Fermat's Last Theorem, developed methods for finding tangents and extrema that anticipated differential calculus, co-founded probability theory with Pascal, and stated the stationary-time principle in optics.
Pierre de Fermat was born in Beaumont-de-Lomagne, near Toulouse, France; the traditional birth year is 1601, though some modern scholarship argues for late 1607 or early 1608 based on parish records — this page follows the traditionally cited year while noting the uncertainty. His father Dominique was a prosperous leather merchant, and his mother Claire de Long came from a family of jurists, giving Pierre entry into the noblesse de robe. He studied law, likely at the University of Toulouse, and spent his working life as a jurist, eventually purchasing a post as a councillor at the Parlement de Toulouse, a high court, where he served for the rest of his career while pursuing mathematics as a private passion.
Fermat rarely published; most of his mathematics survives through correspondence with other scholars and marginal notes in his personal copies of classical texts, above all a copy of Diophantus's Arithmetica. In its margin he wrote his most famous claim, now known as Fermat's Last Theorem — that no positive integers x, y, z satisfy xn + yn = zn for any integer n greater than 2 — noting that he had found 'a truly marvelous proof' too large for the margin; the statement was not proved until Andrew Wiles's work in 1994–1995. Fermat is regarded as the founder of modern number theory, and Fermat's little theorem, on the behavior of integers modulo a prime, remains a basic tool of the subject.
Independently of Descartes, Fermat developed methods of analytic geometry, applying algebra to the study of curves, and he devised a technique for finding tangents and maxima or minima of curves — his methodus de maximis et minimis — that anticipated key ideas of differential calculus decades before Newton and Leibniz. In 1654, in a celebrated exchange of letters prompted by a gambling question, Fermat and Blaise Pascal worked out the basic principles of the mathematical theory of probability. In physics, Fermat formulated what is now called Fermat's principle in optics: light travels between two points along a path for which travel time is stationary. He died on 12 January 1665 in Castres, while carrying out his judicial duties, and was buried in Toulouse.
Workplaces: Parlement de Toulouse (high court of justice)
France