 What axioms should epistemic modal logic include? Well, any tautology of propositional logic should be a theorem, like \(\phi \supset \phi\). For that matter, formulas with the \(K\) operator that are similarly truth-table valid, like \(K \phi \supset K \phi\), should be theorems too. So we’ll just go ahead and make all these formulas theorems in the crudest way possible, by making them all axioms: