tslarm comments on UDT1.01: The Story So Far (1/​10)

[tslarm]

It’s based on a scenario described by Derek Parfit in Reasons and Persons.

I don’t have the book handy so I’m relying on a random pdf here, but I think this is an accurate quote from the original:

Suppose that I am driving at midnight through some desert. My car breaks down. You are a stranger, and the only other driver near. I manage to stop you, and I offer you a great reward if you rescue me. I cannot reward you now, but I promise to do so when we reach my home. Suppose next that I am transparent, unable to deceive others. I cannot lie convincingly. Either a blush, or my tone of voice, always gives me away. Suppose, finally, that I know myself to be never self-denying. If you drive me to my home, it would be worse for me if I gave you the promised reward. Since I know that I never do what will be worse for me, I know that I shall break my promise. Given my inability to lie convincingly, you know this too. You do not believe my promise, and therefore leave me stranded in the desert. This happens to me because I am never self-denying. It would have been better for me if I had been trustworthy, disposed to keep my promises even when doing so would be worse for me. You would then have rescued me.

(It may be objected that, even if I am never self-denying, I could decide to keep my promise, since making this decision would be better for me. If I decided to keep my promise, you would trust me, and would rescue me. This objection can be answered. I know that, after you have driven me home, it would be worse for me if I gave you the promised reward. If I know that I am never self-denying, I know that I shall not keep my promise. And, if I know this, I cannot decide to keep my promise. I cannot decide to do what I know that I shall not do. If I can decide to keep my promise, this must be because I believe that I shall not be never self-denying. We can add the assumption that I would not believe this unless it was true. It would then be true that it would be worse for me if I was, and would remain, never self-denying. It would be better for me if I was trustworthy.)