 Well, perhaps presentists should reject temporal parts and so be endurantists. Must eternalists, who believe in the past and the future, accept temporal parts and so be perdurantists? Or are eternalists free to choose between endurantism and perdurantism?  One reason to think that eternalists should believe in temporal parts is that without them they may have difficulty explaining how things change. How can you both know about theories of persistence (tomorrow) and fail to know about theories of persistence (yesterday)? Presentists don’t seem to have a problem here: your failure yesterday to know about theories of persistence just doesn’t exist. But eternalists are committed to the existence of your two apparently-conflicting states. If eternalists accept temporal parts, they have a neat explanation at hand: your yesterday temporal part doesn’t know about theories of persistence, but your tomorrow part does know about theories of persistence. But if eternalists reject temporal parts, then the two apparently-conflicting states are states of one and the same thing (you), and it’s not obvious how to resolve the conflict. So perhaps eternalists should believe in temporal parts, and, conversely, those who reject temporal parts should be presentists. This argument succeeds only if eternalists really can’t explain change without believing in temporal parts (see  section 3).