Last Friday, Michael Ridge presented a paper at a workshop here in St Andrews on Moral Demandingness.
Ridge discussed obligations entered into collectively by groups of agents - in particular, what happens when one member of the group fails to meet her share of the obligation. He argued that considerations of fairness impose a duty on the remaining parties to divide the extra burden created by this neglect as fairly as possible between them. For instance, suppose I and two friends collectively promise to pay you £9 in return for some service, planning to pay £3 each. Then one of my friends refuses to pay anything. According to Ridge, fairness imposes a duty on you, myself and the remaining friend each to sacrifice the same amount as a result of this refusal. So I and the remaining friend should pay you £4 each, so that you get £8. That way, the cost to each of us of the friend's refusal is £1: you miss out on £1 of your payment and my friend and I pay £1 more than we were supposed to.
There is something appealing about this. But on the other hand there's something appealing about the thought that all that fairness requires of me is that I pay my agreed share of £3. It doesn't seem to be required by fairness (though it may be virtuous and supererogatory) that I pay more than my share (we want to say: more than my fair share) just because someone else has neglected her part in the collective obligation.
So it looks like there's a sense in which fairness requires nothing more of me than that I pay £3, and a sense in which fairness requires that I pay £4. It would be nice to hear more about what these two senses are, in order to lessen the feeling of contradiction. (For what it's worth, my instinct is that the feeling is not genuine.)