 Some philosophers have criticized the label ‘branching time’ as a misnomer, arguing that time does not branch but rather evolves linearly. Early criticism along these lines is found in Rescher and Urquhart (1971), and a similar point is raised in Belnap et al. (2001), who suggest the label ‘branching histories’ instead. This criticism also casts doubt on the appropriateness of the terminology ‘time instants’ used here to refer to the primitive points of the tree. We stick to the terminology for reasons of uniformity. In the branching time literature, the more neutral expression ‘moments’ is prevailing, and in Belnap et al. (2001) the distinction between instants of time and moments is formally worked out: branching time structures are associated with a linearly ordered set of time instants, where an instant is defined as the set of contemporaneous moments contained in different histories.