How much of the person you were at twenty-two is still you?
What it argues
Parfit argues that personal identity is not what matters; what matters is psychological connectedness and continuity, which come in degrees. If he is right, will it be me has no sharp answer, and prudence becomes a question about how much you care about a future person who is partly you.
The probe
List five beliefs or commitments you held at twenty-two. For each, ask whether the person who held it would recognise you as the same person.
The source
Reasons and Persons, Part III — Derek Parfit, 1984. The link goes to the text or to a catalogue record for it, not to a summary. This one is the text itself.