 Against the epistemological optimism of the alchemist who considers himself to be in possession of the perfect science, the skeptic resorts to the traditional arguments of the academic school, emphasizing that certainty is nowhere to be found, as we have only a very partial and superficial knowledge of things. We perceive only the effects and not the profound nature nor the ultimate causes of things. The true essences evade us. The simplest objects (such as a sheet of paper) cannot be completely known, because of the infinite number of relations in which they are involved with other elements of the universe. It has been shown by G. Paganini that these arguments and examples are almost verbatim borrowed from the “second doubt” of Campanella’s Metaphysica, a manuscript that was in Mersenne’s hands at the time he wrote La Vérité des sciences, but that he did not mention as his source (Paganini 2005 &amp; 2008).