  This condition breaks into two parts. The clause requiring that  \(\mathcal{M} , \Delta \Vdash X\) for every \(\Delta \in  \mathcal{G}\) such that \(\Gamma \mathcal{R} \Delta\) is the familiar  Hintikka/Kripke condition for \(X\) to be believed, or be believable,  at \(\Gamma\) . The clause requiring that \(\Gamma \in \mathcal{E} (  t , X)\) adds that \(t\) should be relevant evidence for \(X\) at  \(\Gamma\) . Then, informally, \(t : X\) is true at a possible world  if \(X\) is believable at that world in the usual sense of epistemic  logic, and \(t\) is relevant evidence for \(X\) at that world.