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, the language is conceived as a "special system" in relation to others "in the set of semiological facts". Among different semiological systems, also writing occupies a special place. If there is a real difference between language and writing, we could finally look for it in its power of externalization, which confers to writing a sort of exemplarity among the other institutions. As we’ll 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 differences, can be so considered as a comparative science of institutions. We'll see how this conception of Semiology goes from Saussure to the Geneva School of Semiology.