Numerical and Qualitative Identity
This video presents the same text shown beside it, spoken and on screen. It adds nothing the text does not say.
State
Numerical identity means being one and the same thing; qualitative identity means exact similarity. Personal identity asks about the first, not the second.
Show
Identical twins are qualitatively alike but numerically two. Yesterday's you and today's you are numerically one, however much you changed.
Watch for
Conflating the two wrecks every puzzle ahead—"an identical copy" is never automatically you.