 If you know that \(\phi \supset \psi\) is true, then if you also know \(\phi\), you also know \(\psi\). Or at least, \(\psi\) follows from what you know if \(\phi \supset \psi\) and \(\phi\) do. (The ‘K’ here stands for ‘Kripke’ by the way, not for ‘knowledge’.) Another common axiom shared by all “alethic” modal logics also looks good: