  The challenge, then, is to find a way to capture the non-effects of actions more succinctly in formal logic. What we need, it seems, is some way of declaring the general rule-of-thumb that an action can be assumed not to change a given property of a situation unless there is evidence to the contrary. This default assumption is known as the common sense law of inertia. The (technical) frame problem can be viewed as the task of formalising this law.