 Here is why. A conjunction is known only if its conjuncts are known. So, if \(K(p \wedge(Kp \rightarrow En))\), then \(Kp\). And only truths can be known. So, if \(K(p \wedge(Kp \rightarrow En))\), then \(Kp \rightarrow En\). Of course, \(Kp\) and \(Kp \rightarrow En\) jointly entail \(En\). So theorem 4 is valid, if Fitch’s epistemic resources are. Now, 4 is a theorem, and so, holds in all possible worlds. So its consequent is possible if its antecedent is possible: