In this article, it is argued that rules have two main functions, the practice-defining function and the constraining (fact-to-fact) function. These two functions are compatible. In their function as constraints, some rules are also indirectly regulative. In both of their functions, rules differ from the summaries (rules of thumb) that Rawls discussed and opposed to the constitutive (fact-to-fact) rules which make that some decisions are the right ones. In his work, first on the philosophy of language and later on social ontology, Searle focused on one kind of constitutive rules: counts-as rules, which are constitutive in the sense that they attach new facts to the existence of “old” ones. In doing so, Searle created the scientific interest in constitutive rules which they deserve. However, because of his narrow focus on counts-as rules, Searle also created the impression that counts-as rules are all there is to constitutive rules. This impression is wrong, if only because it overlooks dynamic rules.