 The fifth rule is the crucial one, and is held to be constitutive of assertion. Searle contrasts constitutive rules with regulative  rules.[41]  Constitutive rules, according to Searle, are like definitions: they define what it is to engage in a certain activity: for instance, “attacking the king in such a way that no move will leave it unattacked counts as checkmate” (Searle 1969: 33).