 Proclus was a Pythagorean and Platonic philosopher, the author of two commentaries on Plato’s Timaeus and the Parmenides. For Proclus mathematical objects—and that, of course, included the objects of geometry—were not derived by way of abstraction from sensible particulars, but rather from ideas already contained in the mind. And it was this very kind of “dogmatic” philosophy that Sanches opposed. For Sanches concepts were either unprovable outside of their circular discursive language (e.g., the syllogism), or easily dismissed through the senses, as in the two cases mentioned above. It is for this reason that one can justly qualify Sanches’ philosophy as being empiricist and sceptical at once. Clavius, the addressee of the letter, was clearly against of the sceptics’ conception of knowledge. Chikara Sasaki writes: 