This is genuinelly, for me, one of the most interesting questions I've ever come across. Normally it's answers that are interesting, not the questions, but this is not only an interesting question but also one of the most interesting things I know of.
A thought experiment:
There is an eccentric trillionaire who puts a vial of painful fatal poison in front of you and offers you £1 billion if you agree to drink it. But you don't actually have to drink it now; if you agree then the trillionaire will give you the money, you go away, you come back in one month and you drink the poison then. If at any time during that month you change your mind, fine. You don't have to go through with it and, this is the important bit, you *CAN KEEP THE MONEY*.
In other words, all you have to do to get £1 billion is to say yes you will drink the poison, wait for the cheque to clear, then turn round and say no.
Knowing that this is an option for you, knowing you can take the money and then change your mind ... is it possible for you to ever *genuinelly mean* to drink the poison?
Let's face it, we probably would all say yes, take the money and then say no.
But would that be a genuine change of heart? Or would we always have at least some doubt when we first said yes?
This is not a question of what would you do, it's about what's going on in your mind.
The question was first posed as an exercise in logic and using the mathematics of logic and calculation, it's logical to say yes, get the money and then say no. A rational person would accept the money but only an irrational one would drink the poison. So to ever actually go through with it, you have to be both rational and irrational. In other words, it's a paradox.
BUT ... ! From a psychological point of view, human beings ARE both rational and irrational. So a human being will happily take the money then say no. So from a psychological point of view, the question becomes whether or not you can HONESTLY take the money in good conscience or will you only ever do so because of the get out clause?