  In fact, formula (2) is behind many of the problems of logical  omniscience. It asserts that an agent knows everything that is  implied by the agent’s knowledge—knowledge is closed under  consequence. While knowable-in-principle, knowability, is closed  under consequence, the same cannot be said for any plausible version  of actual knowledge. The distinction between (1) and (2) can be  exploited in a discussion of the paradigmatic Red Barn Example of  Goldman and Kripke; here is a simplified version of the story taken  from (Dretske 2005).