Full Idea
Suppose a brave officer, flogged as a boy for robbing an orchard, to have captured a standard in his first campaign, and become a general in advanced life. [If the general forgets the flogging] he is and at the same time is not the same as the boy.
Gist of Idea
Boy same as young man, young man same as old man, old man not boy, if forgotten!
Source
Thomas Reid (Essays on Intellectual Powers 3: Memory [1785], III.Ch 6)
Book Reference
'Personal Identity', ed/tr. Perry,John [University of California 1975], p.114
A Reaction
The point is that strict identity has to be transitive, and if the general forgets his boyhood that breaks the transitivity. If identity is less strict there is no problem. The general may only have memories related to some part of his boyhood.