Subjunctive analyses of what we ought to do often appeal to what we would do (or what we would want ourselves to do) if we were both fully informed and fully rational. Many such analyses commit what is called the Conditional Fallacy and are, therefore, subject to counterexample. The counterexamples all involve cases where full information (and/or full rationality) affects what one has reason to do and, thus, what one ought to do. To illustrate, consider the following very simple analysis:
(SA) S ought to do x in C iff a fully rational and fully informed version of S would want to do x in C.
To see that this analysis commits the Conditional Fallacy, suppose that S is facing a choice of picking only one of either box A or box B. One contains a very large sum of money and the other contains none at all. In C, S has no information about which box contains the money, but, in C, S can perform x, which is the act of S’s paying a small sum of money to peek inside each box. Now, a fully informed and fully rational version of S (viz., S+) would not want to perform x, because doing so costs money and, being fully informed, S+ would learn nothing by peeking inside them. But clearly S ought to do x in his current uninformed state. So SA fails due to this counterexample.
The problem arises because coming to have full information and/or coming to be fully rational can itself affect what one has reason to do. So, we should give our subjunctive analyses, not in terms of full information (that is, knowledge of all the facts), but in terms of knowledge of only the relevant facts. What are the relevant facts? Well, let C be S’s actual circumstances and let C+ be exactly like C except that, in C+, S knows that p. For any proposition p, that p is a relevant fact for S in C iff S’s objective reasons for action in C+ do not differ from S’s objective reasons for action in C. Clearly, then, neither the fact that the money is in box A nor the fact that there is no money in box B are relevant facts, for knowledge of these fact would affect what one has reason to do. So an S that knew only the relevant facts (viz., S*) would still want to do x.
Instead of SA, then, perhaps we should adopt something like the following analysis (Doug’s analysis):
(DA) S ought to do x in C iff S would want S to do x in C if S were informed of all relevant facts and if S were to respond appropriately to the reasons that those facts provide, coming to desire only what S has, given the relevant facts, sufficient reason to want as well as coming to desire everything that S has, given the relevant facts, decisive reason to want.
I know that there are other ways of potentially avoiding the Conditional Fallacy, but I wonder if this one is satisfactory. This is all just preliminary and very half-baked. I have a lot to read still on this sort stuff, but I just want to know whether this is a non-starter or not. Thoughts?