The essay aims to show how custom, the use with its “barriers” for Montaigne, is implicitly or explicitly present in all other external regulatory instances: positive religions and their system of rewards and punishments, laws and the penal device that is incorporated in them, the moral precepts and the behaviors they require, the social rewards, the science itself in some ways, cannot be separated from a set of collective beliefs, practices and representations of which the coutume is the keystone. These rules are, in a certain sense, the concrete forms that each time take la coutume. It can be said that Montaigne’s discourse on custom is in fact placed along a double divergent line: that of criticism and that of praise. On the one hand, the coutume has no authority of its own, on the other, in the absence of anything better, it sees itself recognized as a social function of rule and, indeed, as a “rule of rules”.