The Saussurian notion of semiology is closely linked to that of institution. In fact, in Saussure’s words, “systems of signs” are “social institutions”. Furthermore, language is conceived as a “special system” in relation to others “in the set of semiological facts”. Among different semiological systems, writing also occupies a special place. If there is a real difference between language and writing, we could look for it in the power of externalization, which confers to writing a sort of exemplarity among the other institutions. As we will see in this article, writing reveals the process of institutionalization itself, as well as the rational sociality of reasoning institutions and the irrational sociality of unreasoning institutions as languages. Semiology, which is the discipline studying these phenomena and their diferences, can be considered as a comparative science of institutions.