We address the problem of rough applicability of rules within the framework of approximation spaces. The graded applicability of a rule for an object of an approximation space, introduced here, is viewed as a fundamental form of rough applicability. It is based on the graded meaning of a set of formulas, defined in our previous works. The notion of graded applicability enjoys a number of interesting properties and it is useful – in our opinion – in modeling of rule-based complex systems like multi-agent systems.