 Taking an axiomatic approach to specifying the logic, however, yields a presentation in terms of easy to grasp principles. To start with the simplest, then the principle T states that knowledge is factual: If the agent knows \(\varphi\), then \(\varphi\) must be true. The more cumbersome K states that if the agent knows an implication, then if the agent knows the antecedent, it also knows the consequent. I.e., if we include the derivation rule modus ponens (from \(\varphi\rightarrow\psi\) and \(\varphi\), conclude \(\psi\)) as rule of our logic of knowledge, K states that knowledge is closed under implication. The principle B states that if \(\varphi\) is true, then the agent knows that it considers \(\varphi\) possible. Finally, 4 states that if the agent knows \(\varphi\), then it knows that it knows \(\varphi\). T, B and 4 in the table below (the names are historical and not all meaningful).