 This letter of August, 1641, can be found in Correspondance du P. Marin Mersenne, religieux minime. X, Du 6 août 1640 à fin décembre 1641 (1967: 730) wherein the author praises Sanches’ ingenious exaggerations concerning the possibility of acquiring perfect knowledge, and criticizes Cartesianism for not being able to advance (“non progreditur”) beyond its “hyperbolical doubt” (1967: 730) . But again, the letter is too late to serve as proof of Descartes’ knowledge of Sanches’ treatise prior to the writing and publication of the Discourse. Its intended target seems to have been an objection to the perceived scepticism of the Meditations. Thus, if Mersenne informed Descartes of Huebner’s letter comparing his work to that Sanches’s, then the letter would only have apprised Descartes that he was being compared with the Iberian “Pyrrhonist”, which would not have made Descartes very happy, given that by this time he had grown tired of answering objections and trying to explain why his method was instead intended to dispel scepticism and ground a science on clear and distinct ideas (Mullin 2000: 8). Therefore, if we can imagine Descartes being upset about being compared with Sanches, one can at least partially understand why he would be so, and would “refuse” to answer the objection (Mullin 2000: 8). It has been conjectured, for instance, that Descartes might have been thinking of Sanches when he wrote in the Discourse that the reason for his undertaking was not to imitate or to copy “the sceptics, who doubt only for the sake of doubting” but rather “to reach certainty” (1637 [PWD: 125]). Significantly, while most scholars of Sanches’ work have noted the similarities between Sanches and Descartes, for others like Joseph Moreau (1960) and Joaquim de Carvalho (1955), there are significant differences. These similarities displayed in two parallel columns in the introduction to Sanches’ Opera philosophica (1955: xxx–xxxiii), merely establish, argues Carvalho, a “correlation of words” (1955: xxxiii, my translation). One important difference between the two thinkers, says Carvalho, is that although Sanches doubts our perfect knowledge of external things, he never doubts their existence. This obviously was not the case for Descartes, for whom the search for certainty was the search for whatever knowledge could be acquired through the light of reason, and not through the senses. Thus for Moreau one major difference between them was their opposing views concerning the truths of mathematics (1960: 30–34): for Sanches a posteriori and dubitable; for Descartes a priori and indubitable. What they did share was a rejection of the Scholastic appeal to external authority. For Descartes, the opinions of others could never lead to the kind of certainty only a mind (cogito) reflecting on the content of its own thoughts could reach; and for Sanches the opinions of scholarly authorities—however illustrious—did not help us to arrive at perfect knowledge. The assumed “knowledge” of the authorities was derived from syllogistic and demonstrative logic, which depended on the circularity of its definitions and premises (verba) to arrive at their conclusions concerning things (rerum). More often than not, these Aristotelian scholars with their verbal gymnastics created great confusion out of what was otherwise clear, even to a child.