 For such a case would satisfy the above constraints. But it is a case in which A is perceived by an observer both as following, and as being followed by, B, and we know that such a case never occurs in experience. ‘Is perceived by x as followed by’ is an asymmetric relation (assuming we are dealing with a single sense modality), and so one that can be grounded in the causal relation only if the causal relation is itself asymmetric. Now if perspectivalism cannot meet the challenge to explain why, when B is perceived as following A, A is never perceived by the same observer as following B, it seems that our experience of time order, insofar as it has a causal explanation, requires causation to be objectively asymmetric.