  The main obstacle to doing this is the monotonicity of classical logic. In classical logic, the set of conclusions that can be drawn from a set of formulae always increases with the addition of further formulae. This makes it impossible to express a rule that has an open-ended set of exceptions, and the common sense law of inertia is just such a rule. For example, in due course we might want to add a formula that captures the exception to Axiom 3 that arises when we move an object into a pot of paint. But our not having thought of this exception before should not prevent us from applying the common sense law of inertia and drawing a wide enough set of (defeasible) conclusions to get off the ground.