Default theories

Default theories are frameworks used in logic and artificial intelligence to model reasoning that involves assumptions or common knowledge, which are generally true but may have exceptions. They allow a system to make plausible conclusions based on typical situations unless there's specific information indicating an exception. For example, one might default that "birds can fly" but can also recognize exceptions like penguins. Default theories help machines reason in a way similar to humans, filling in missing information with reasonable assumptions while allowing for special cases.