Diachronic and synchronic unity

There are two different varieties of question concerning the unity of consciousness: questions about unity at a time, and unity over time. A recent trend in the debate about unity has been to attempt to provide a ‘generalized’ account that purports to solve both problems in the same way. This attempt can be seen in the accounts of Barry Dainton and Michael Tye. In this paper, I argue that there are crucial differences between unity over time and unity at a time that make it impossible to provide a generalized account of unity. The source of these crucial differences is the phenomenon of the ‘continuity of consciousness’. I argue that accounts of unity over time have to provide an account of this continuity, and that there is no phenomenon analogous to continuity in the case of unity at a time. Attention to the continuity of consciousness reveals crucial structural differences between the two varieties of unity. These structural differences make it impossible to provide a generalized account of unity. I show that the problems faced by Dainton’s and Tye’s accounts in the light of the structural differences make their accounts of unity appear far less appealing than they might initially have looked. I conclude by noting that, in the light of the important differences between the two varieties of unity, it is a mistake to attempt to model accounts of unity over time on accounts of unity at a time.