Full Idea
No thought, considered as at different times, can be the same, each part thereof having a different beginning of existence.
Gist of Idea
No two thoughts at different times can be the same, as they have different beginnings
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 2.27.02)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.329
A Reaction
cf Reid's objection (Idea 1368). Presumably there could be type-identity? If I have a thought which is identical to the thought I had yesterday, how do I tell whether it is the same token or merely the same type? It fails Locke's introspection test.
Related Idea
Idea 1368 Locke mistakes similarity of a memory to its original event for identity [Reid on Locke]