 The A-series essentially amounts to a characterization of time and temporal order in terms of past, present, and future. The B-series, in contrast, is based on the notions ‘earlier’ and ‘later’. Thus, whereas the A-series presupposes a distinguished present, the B-series involves an overarching, global perspective on time. McTaggart argued that the B-series is insufficient because it lacks an appropriate notion of change, and he rejected the A-series as inconsistent because what is future now will be past, which, according to him, requires that one and the same time instant has incompatible properties. From this he concluded that time is unreal. For a detailed discussion of McTaggart’s account and its philosophical relevance, see Ingthorsson (2016) and the entry on  time.