Although he was born in Tui, in Galicia, Spain, Sanches was baptised in Braga, Portugal, on July 25, 1551, and spent his childhood there. His father was the Spaniard Antonio Sánchez, also a physician; and his mother Filipa de Sousa was Portuguese. Being of Jewish origin, even if converted, he was legally considered a New Christian.
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.
Statue of Francisco Sanches, by Salvador Barata Feyo in Braga.
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 human capabilities because of the nature of objects and the nature of man. The interrelation of objects, their unlimited number, and their ever-changing character prevent their being known. The limitations and variability of man's senses restrict him to knowledge of appearances, never of real substances. In forming these last argument he drew on his experience of Medicine to show how unreliable our sense experience is.
Sanches' first conclusion was the usual fideistic one of the time, that truth can be gained by faith. His second conclusion was to play an important role in later thought: just because nothing can be known in an ultimate sense, we should not abandon all attempts at knowledge but should try to gain what knowledge we can, namely, limited, imperfect knowledge of some of those things with which we become acquainted through observation, experience, and judgment. The realization that nihil scitur ("nothing is known") thus can yield some constructive results. This early formulation of "constructive" or "mitigated" skepticism was to be developed into an important explication of the new science by Marin Mersenne, Pierre Gassendi, and the leaders of the Royal Society.
Reproduction of Francisco Sanches' signature as found in his diploma from the University of Montpellier. It reads, in Latin, Franciscus Sanches Bracharensis, or Francisco Sanches of Braga. From the statue by Salvador Barata Feyo.
Carmen de Cometa, 1577.
Quod nihil scitur, 1581.
De divinatione per somnum, ad Aristotelem, 1585.
Opera Medica, 1636, which includes:
De Longitudine et Brevitate vitae, liber
In lib. Aristotelis Physiognomicon, Commentarius
De Divinatione per Somnum
Quod Nihil Scitur, liber
Tractatus Philosophici, 1649.
^João-Maria Nabais, A diáspora de Francisco Sanches, na busca da consciência do Eu. Assistente Hospitalar Graduado; Universidade de Lisboa, p. 359, online.
SANCHEZ, Franciscus (2007), Daß nichts gewußt wird - Quod nihil scitur, Hamburg: Meiner Verlag, ISBN978-3-7873-1815-5 Latin-German. Introduction and Notes by Kaspar Howald. Translated by Damian Caluori and Kaspar Howald. Latin Text by Sergei Mariev. PhB 586. 2007. CLXIV 322 pages.
SANCHEZ, Francisco; Limbrick, Elaine. Introduction, Notes, and Bibliography; Thomson, Douglas F.S. Latin text established, annotated, and translated. (1988), That Nothing is Known, Cambridge: Cambridge University Press, ISBN0-521-35077-8 Critical edition of QVOD NIHIL SCITUR.
SANCHEZ, Francisco; Buccolini, C., Lojacono, E. Latin text and Italian translation, with Introduction, Notes, and Bibliography (2011), Tutte le opere filosofiche, Milano: Bompiani, ISBN9788845267246.
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CALUORI, Damian, 'The Scepticism of Francisco Sanchez'. Archiv für Geschichte der Philosophie 89 (2007) 30-46.
CARVALHO, Joaquim de, Introdução a Francisco Sanches, in Francisco Sanchez, Opera Philosophica, Coimbra, 1955.
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PINTO, Sérgio da Silva, Braga et Francisco Sanches: discours prononcé à l'Université de Toulouse, à la séance solennele des commemorations du IVème centenaire de Francisco Sanchez, le 12 Juin 1951, Braga: Cruz, 1951.
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SÁ, Artur Moreira de, Raízes e projecção do pensamento de Francisco Sanches, Braga: University of Braga, 1955.
SÁ, Artur Moreira de, Francisco Sanches, Filósofo e Matemático, Lisboa, 1947.
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TAVARES, Severino, Lúcio Craveiro da SILVA, Diamantino MARTINS and Luís de PINA, Francisco Sanches, no IV centenário do seu nascimento, Braga: University of Braga, 1951.