 Unified consciousness at a given time (synchronic unity) has mainly been our topic so far. We now turn, more briefly, to unified consciousness over time (diachronic unity). As was noted as long ago as Kant, unity across time is required even for such rudimentary mental operations as counting (1781: A103); indeed, unity across time is crucial for virtually all cognition of any complexity. Now, unification in consciousness might not be the only way to unite earlier cognitive states (earlier thoughts, earlier experiences) with current ones but it is certainly a central way and the one best known to us. 