This paper analyses the available eyewitness accounts and documents relating to the young Francisco Sanchez’s sojourn in Italy with the aim of highlighting the influence of this experience on his education and on his particular form of scepticism. The issue of the certainty of geometry, addressed in his letter to Clavio, is an example of a theme that the Portuguese philosopher must have picked up from a typical debate in Italian academic circles at that time. Even more enlightening for an exact understanding of his Quod nihil scitur, however, are the contemporary discussions on the epistemological status of medicine and on the reliability of traditional Galenic pathology. They show that, instead of being the expression of a radical lack of confidence in every form of knowledge, nihil sciri denotes simply a rejection of the perfect cognition of things and a receptiveness towards a model of ‘weaker’ knowledge, inspired precisely by the exercise of medical practice.
Keywords: Francisco Sanchez, scepticism, medicine, geometry, Clavio, science