But the persistence concerns a numerical identity (a same), and the invariability concerns the qualitative identity
(something that does not change over time), which would mean that the immediate and analytical inference to be made from the numerical identity to the qualitative identity
, will fail on the logical plan.
In this regard, it has been customary to distinguish between numerical and qualitative identity
: over the course of an individual's life there will be significant qualitative changes, for example, in terms of beliefs and memories; however, these changes are consistent with the notion that it is one and the same person over time.
Sider uses this example to introduce the problem of personal identity and to explain the distinction between quantitative and qualitative identity
. He then uses the rest of the chapter to provide a more than adequate summary of various historical approaches and their associated strengths and weaknesses.