It has been notoriously difficult to say what makes a person the same person over time, especially given then enormous physical and psychological changes that a person undergoes. In the span of a decade, a person can completely reform their beliefs, their values, and their patterns of action, and can even suffer total memory loss. It seems natural to say, as Derek Parfit does, that they are not really “the same person”, but rather they are connected to that past person, only insofar as they share that past person’s psychology. They are thus (say) 25% connected, and that former person survives only to this small degree.
Let’s assume that Polanski is significantly different in this way: that he is no longer Polanski1973, that person’s youthful immorality and disregard has been completely wiped out and replaced with kindness and thoughtfulness. The former criminal only survives to some small extent (say, 25%, though the number doesn’t really matter).
As Bernard Williams quickly pointed out, even under these questionable assumptions, there is something seemingly absurd in attempting to apply this result to the question of his responsibility for a 30 year-old rape. Parfit’s theoretical model has absurd practical implications: that Polanski only ought to be sentenced to 25% of the normal jail time, for example. It is just as absurd to suggest that a person who owes you $10000 should only pay $2500 if she undergoes the same kind of change over time, or that you are no longer married to someone if Alzheimer’s decimates their mind.
Yet, the task remains: how do we ground this unwavering identity over time? What does it consist in? Without an answer, our practices of prosecution and punishment (which I generally support, especially in this case) can start to look downright strange. For if there is not much of Polanski left to punish, then who the hell are we going after?