 In lieu of epistemological intuitions, we could discuss a concept of knowledge by discussing these and other principles. Should we accept T as a principle that knowledge follows? What about the others? Before we proceed, let us first make clear how the four above principles relate to the indistinguishability interpretation. To do so, we need the notion of a normal modal logic. In the below definition, as in the above principles, we are technically using formula schemas. For example, in \(K_{a}\varphi\rightarrow\varphi\), the \(\varphi\) is a variable ranging over formulas in \(\mathcal{L}_{K}\). Thus, strictly speaking, \(K_{a}\varphi\rightarrow\varphi\) is not a formula, but a scheme for obtaining a formula. A modal instance of \(K_{a}\varphi\rightarrow\varphi\) is then the formula obtained by letting \(\varphi\) be some concrete formula from \(\mathcal{L}_{K}\). For example, \(K_{a}p\rightarrow p\) and \(K_{a}(p\wedge K_{a}q)\rightarrow(p\wedge K_{a}q)\) are both modal instances of T.