  Self-referentiality of justifications is a new phenomenon which is  not present in the conventional modal language. In addition to being  intriguing epistemic objects, such self-referential assertions  provide a special challenge from the semantical viewpoint because of  the built-in vicious circle. Indeed, to evaluate \(c\) one would expect first to evaluate \(A\) and then assign a justification  object for \(A\) to \(c\). However, this cannot be done  since \(A\) contains \(c\) which is yet to be evaluated.  The question of whether or not modal logics can be realized without  using self-referential justifications was a major open question in  this area.