Full Idea
Locke's mistake arises because he confuses the 'same' consciousness of past events. A memory is only the 'same' in the sense of being similar, not in the sense of complete identity.
Gist of Idea
Locke mistakes similarity of a memory to its original event for identity
Source
comment on John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 2.27.10) by Thomas Reid - Essays on Intellectual Powers 3: Memory Ch 6
Book Reference
'Personal Identity', ed/tr. Perry,John [University of California 1975], p.117
A Reaction
cf Locke's point in Ideas 1197 and 1373.
Related Ideas
Idea 1197 No two thoughts at different times can be the same, as they have different beginnings [Locke]
Idea 1373 Identity over time involves remembering actions just as they happened [Locke]