A conundrum by Oxford philosopher Derek Parfit:

In several years, a young Russian will inherit vast estates. Because he has socialist ideals, he intends, now, to give the land to the peasants. But he knows that in time his ideals may fade. To guard against this possibility, he does two things. He first signs a legal document, which will automatically give away the land, and which can be revoked only with his wife’s consent. He then says to his wife, ‘Promise me that, if I ever change my mind, and ask you to revoke this document, you will not consent.’ He adds, ‘I regard my ideals as essential to me. If I lose these ideals, I want you to think that I cease to exist. I want you to regard your husband then, not as me, the man who asks for this promise, but only as his corrupted later self. Promise me that you will not do what he asks.’

She agrees. In time the Russian’s ideals fade, and when he inherits the land he asks his wife to revoke the document, declaring that he releases her from her earlier commitment. What is her obligation here? She had made her promise to her earlier husband, but is that a different person from the man before her now? In her view, the man to whom she made her promise no longer exists, and so cannot release her from her obligation. Is this right? If a person is a succession of earlier and later selves, does a promise attach to a person or to a self?

(Derek Parfit, Reasons and Persons, 1984. See The Ulysses Contract.)