Francisco Sanches, a philosopher and physician, was born on the Spanish-Portuguese border, either in Tuy or Braga, of Marrano or New Christian parents. His family had moved to Portugal and then to southern France to escape religious and political persecution. The young Sanches studied at the Collège de Guyenne in Bordeaux, the same school that his distant cousin, Michel Eyquem De Montaigne, attended. Sanches studied in Rome and then went to the University of Montpellier, where he received a degree in medicine in 1574. He was appointed professor of philosophy in 1585 and professor of medicine in 1612 at the University of Toulouse, where he had a successful career until his death in 1623.

One of Sanches's first philosophical writings that has survived is a letter to the Jesuit mathematician, Father Christopher Clavius, who had just edited Euclid's works and whom Sanches had met in...