The system of logic plays a central rôle in Leibniz's methodology of science. According to his basic ideas, any scientific question should be posed in the form "Is S a P?"and its answer might be found either in Encyclopcedia Universalis of the human knowledge (when the fact is synthetic) or in the corresponding relation between Numeri Characterici of S and P (when the fact is analytic). Leibniz believed that "a few selected men", as he wrote, could systematize (in a quinquenium!) all data and establish a correspondence between the elementary notions and their characteristic numbers. As we see, the logical system determines both the formal translation of the scientific sentences and the mechanism of checking their truthfulness.