Francisco Sanches (also spelled Sánchez in contemporary sources; c. 1550 – November 16, 1623) was a skeptic, philosopher and physician of Sephardi Jewish origin, born in Tui, Spain (although he was baptized in Braga, Portugal). Early life and academic career In the auditorium of the University of Toulouse there is a portrait of Francisco Sánchez, which bears the following inscription: "Francisco Sanchez Lusitanus". Although the investigations carried out by Henry Pierre Cazac at the beginning of the 20th century – he presented, among other documents, an autograph by Sánchez that reads as follows: "Ego, Franciscus Sanctius, Hispanus, natus in civitate Tudensi [...]" – showed the Spanish origin of Francisco Sánchez, there has been a long controversy around his nationality, as shown in the title of some publications that try to ascribe the name of the illustrious doctor and philosopher to the French Renaissance (The Skeptics of the French Renaissance, by John Owen) or Portuguese (Francisco Sanches ea dúvida methodica na Renascença portuguesa, doctoral thesis by Evaristo de Moraes Filho). His father was the Spaniard Antonio Sanches, also a physician; his mother Filipa de Sousa was Portuguese. Being of Jewish origin, even if converted, he was legally considered a New Christian. He studied in Braga until the age of 12, when he moved to Bordeaux with his parents, fleeing the surveillance of the Portuguese Inquisition. There he resumed his studies at the College de Guyenne. He went on to study medicine in Rome in 1569, and, back in France, in Montpellier and Toulouse. He ended up, after 1575, as a professor of philosophy and medicine at the University of Toulouse. Main work and thought In his Quod nihil scitur (That Nothing Is Known), written in 1576 and published in 1581, he used the classical skeptical arguments to show that science, in the Aristotelian sense of giving necessary reasons or causes for the behavior of nature, cannot be attained: the search for causes quickly descends into an infinite regress and so cannot give certitude. He also attacked demonstrations in the forms of syllogisms, arguing that the particular (the conclusion) is needed to have a conception of the general (the premises) and thus that syllogisms were circular and did not add to knowledge. Perfect knowledge, if attainable, is the intuitive apprehension of each individual thing. But, he then argued, even his own notion of science (perfect knowledge of an individual thing) is beyond