The (Most) Rational Thing to Do The (Most) Rational Thing to Do

It is particularly tempting to classify this version of future Tuesday indifference as a case of irrationality because the connection between the judgments that the agent accepts (that all future pains are bad) and the conclusion that he fails to accept (that he has reason to avoid pains on future Tuesdays) is so close that it is dif~cult to see how he could accept one without accepting the other. There is little room for confu- sion, for failure to follow the steps of an argument, or for substantive disagreement. The same would be true of a person who purports to believe that A and that if A then B, but denies that this gives any reason to believe B (or denies that it gives such a reason on Tuesdays). But there is also a more general tendency to lump together, as “require- ments of rationality,” two kinds of requirements that should, I believe, be kept distinct. Requirements of the ~rst kind specify the form that our thinking must take if we are to avoid the charge of irrationality. Requirements of the second kind specify what we have most reason to do, hence what we would do if we were “ideally rational.”10_Accounts

of the latter kind are often referred to as “conceptions of rationality,” but I believe that they are more appropriately seen as substantive conceptions of the reasons that we have.11

The distinction between the two is well illustrated by the idea that there is a rational requirement to give weight to one’s future interests. There certainly are some cases in which a person’s failure to give weight to his or her future interests is irrational. These are cases in which a person judges that these considerations are reasons but then fails to take them into account in deciding what to do, or fails to give them the weight that he or she judges them to have. This is what is usually going on when we fail to _oss our teeth, to fasten our seat belts, or to do other things that we can see we have reason to do because they will promote our present or future aims. Cases of this kind are ex- tremely common, and this may explain the widespread tendency to cite failure to give weight to considerations of one’s own well-being as the prime example of irrationality.

But not every failure to give weight, or to give proper weight, to one’s future interests is an instance of irrationality. It is, for example, a matter of controversy how one’s future interests should be taken into account in present decisions—whether these interests should be “dis- counted” because of their remoteness in time and if so at what rate. This may be called a debate about “rationality,” but this label is appropriate only if what is meant is that it is a debate about what we have most reason to do, or what we would do if ideally rational. A person who believes, on general theoretical grounds, that her future interests should be sharply discounted, and who acts accordingly, may be making a mistake about the reasons that she has, but this does not make her irrational, any more than it does a person who accepts a fallacious argument or makes some other mistake about reasons. One might of course stipulate that “irrationality” simply means acting contrary to one’s interests. But such a stipulation has the effect of giving one class of reasons special status as far as rationality and irrationality are concerned. Given that there are reasons for action other than those provided by an agent’s own interests, I see no justi~cation for giving this one class of interests such special status.

Another area in which “requirements of rationality” in the two senses just distinguished are often run together is in claims made for axiomatic theories of rational choice.12_{People often violate these axi-}

oms by making mistakes in probabilistic reasoning, or by failing to see that the complex gamble they have chosen is dominated by another alternative (that is to say, that this alternative would be better from their point of view, no matter which of the uncertain states turns out to be realized).13_{But these mistakes do not deserve the name of irra-}

tionality any more than accepting a fallacious proof or making some other error in calculation does. Decision theory should thus be under- stood as presenting requirements of rationality in the second sense I distinguished: that is to say, as offering a partial account of what one has most reason to prefer, and hence would prefer if one were “ideally rational.” More speci~cally, the axioms of such a theory state consis- tency conditions that our choices, and judgments of desirability and probability, would meet if we were perfectly rational, just as a system of deductive logic states consistency conditions that would be ful~lled by the beliefs of an ideally rational person. Violating conditions of either of these kinds leaves one open to rational criticism: criticism that is of a particularly clear and uncontroversial kind since it does not depend on any substantive claims about the truth of particular state-

ments or the desirability or probability of particular outcomes. But this relatively uncontroversial character is not accurately described by say- ing that although other mistakes leave one open to criticism, violating these conditions amounts to irrationality. It is not, after all, always irrational to have inconsistent beliefs or to reject a claim that (although one does not realize it) follows logically from other things one holds.

The axioms of rational choice theory provide only a partial account of ideal rationality, since they state only conditions of consistency and since these conditions apply only to reasons for promoting certain states of affairs or for wanting them to occur. A full account of what an “ideally rational” agent would do could involve at least three possible dimensions of idealization, in the directions of (1) possession of full information about one’s situation and the consequences of possible lines of action, (2) awareness of the full range of reasons that apply to someone in that situation, and (3) _awless reasoning about what these reasons support. The most fully ideal notion of “the (most) rational thing to do” would thus be “the course of action that is best supported by all the relevant reasons given a full and accurate account of the agent’s actual situation.” Given the great variety of reasons for action, it seems to me very unlikely that there could be such a thing as a theory of reasons in this sense—that is to say, a systematic, substan- tive account of what we have most reason to do.14