 We assign \(\Box_aF\) the reading “agent a defeasibly knows F”. This is a weak notion of knowledge studied by Lehrer and Paxson (1969) and by Lehrer (1990, 2000) and formalized by Stalnaker (1980, 2006). Intuitively, defeasible knowledge of F is belief in F that persists upon receipt of any further true information: the agent believes F and, if told any further true information, she will continue to believe F. Defeasible knowledge is sometimes also called “safe belief”. 