Claims can be false but to know something means that a person believes it and it is true in this kind of logic at least . So in epistemic logic Kp p by definition . Therefore Kp p is not possible . For believes B is used . And in most epistemic logics Bp p Kp is an axiom . So it might not be obvious , but it is a rule in most epistemic logics . EDIT Definition p means that p is possible . There is a possible world where p is the case . Definition p means that p is necessary . In all possible worlds p is the case . EDIT 2 Ok , I ' ve read the entire argument and I believe I understand it . So the argument presupposes A , B , C and D as rules of the logic which are normal rules , but I can explain them if you ' d like . Then the argument assumes KP and NonO and shows that this leads to a contradiction . I see no problem with this argument . So if you have questions I might be able to help . EDIT 3 Of course I do not believe that this in any way is a proof of the existence of a god .