 Just as everything else that has to do with Sanches, there is even uncertainty as to the date the Letter to Christopher Clavius was written. Raymond Delassus, Sanches’ disciple, and first biographer, dates the letter to around 1575, while J. Iriarte believes that the latter was written much later, in 1589, in which case it would place the writing of the letter at least eight years after the publication of Quo nihil scitur (1581). Given, however, that Clavius’ translation and commentary on Euclid’s Elements was published in Rome in 1574, it would seem that the former date of 1575, makes much more sense. It stands to reason that Sanches would have responded to Clavius’ commentary soon after its publication rather than fifteen years later, especially when so much of what is in the letter is implicitly related to Sanches’ epistemology in Quod nihil scitur. In that sense the Letter to Clavius constitutes a debate between those who like Clavius believed that the truths of mathematics were a priori and indubitable, and thinkers like Sanches who held an anti-Platonist, empiricist view of the world. A few quotes from Clavius’ Opera mathematica and from Sanches’s Letter help us to understand the debate. Clavius wrote: