Full Idea
Kant thought that personal identity could not simply consist in sameness of consciousness, since someone's consciousness might be qualitatively similar to that of someone else who had existed previously.
Gist of Idea
Two persons might have qualitatively identical consciousnesses, so that isn't enough
Source
comment on John Locke (Essay Conc Human Understanding (2nd Ed) [1694]) by Immanuel Kant - Critique of Pure Reason
Book Reference
'Personal Identity', ed/tr. Martin,R /Barresi,J [Blackwells 2003], p.60
A Reaction
An interesting point, which leads to the question of whether two conscious events must by type-identical or token-identical to confer identity over time. Locke implies type- (which leads to Kant's objection). He needed, but couldn't have, token-.