  A large part of the qualitative dynamics that is needed for planning consists in inferring what does not change. Take a simple plan to type the word ‘cat’ using word processing software:  the natural plan is to first enter ‘c’, then enter ‘a’, then enter ‘t’. Part of one’s confidence in this plan is that the actions are independent: for instance, entering ‘a’ does not also erase the ‘c’. The required inference can be thought of as a form of inertia. The Frame Problem is the problem of how to formalize the required inertial reasoning.