 While Prior himself favored Peirceanism, the Ockhamist branching time temporal logic, which he developed as a possible alternative, has been gaining much more influence in the literature on branching time. In the Ockhamist branching time logic OBTL, truth is not only relativized to a time instant in the tree but also to a history passing through that instant, and the future operator \(F\) is now evaluated along the given history. Thus, the intuitive meaning of \(F\) becomes “With respect to the given history, it will be the case that \(\dots\)”. In addition to the temporal operators \(F\) and \(P\), the language of OBTL contains a modal operator \(\Diamond\) and its dual \(\Box\), which are interpreted as quantifiers over histories. Given a set of atomic propositions \({PROP}\), the set of formulae of OBTL can be recursively defined by