Rational Desire and Rationality in Desire: An Unapologetic Defense Peter Railton Preliminary draft of October 2008—please do not circulate without permission Introduction Consider Robert Stalnaker’s well-known, elegant formulation of the interlocking, functional nature of belief and desire: Belief and desire … are correlative dispositional states of a potentially rational agent. To desire that P is to be disposed to act in ways that would tend to bring it about that P in a world in which one’s beliefs, whatever they are, were true. To believe that P is to be disposed to act in ways that would tend to satisfy one’s desires, whatever they are, in a world in which P (together with one’s other beliefs) were true. [Stalnaker (1984), 15; emphasis added] This characterization gives a picture of a potentially rational agent as, so to speak, at the mercy of his beliefs and desires, whatever they are. Whether an individual agent is actually rational, one might naturally think, will depend on what fills in for ‘whatever they are’—for this will determine the shape of her life and, roughly, who, if anyone, is in charge. Put another way: Autonomy will depend heavily on how ‘whatever they are’ is filled in—what role does the agent herself play? And rationality will depend heavily on what is filled in—will the agent’s beliefs and desires be as they rationally should be?1 The thought is: If your beliefs and desires are as they rationally should be, and you as agent have played the right sort of role in acquiring them, then insofar as they are functioning normally—namely, as Stalnaker indicates—to guide how you act, then your actions, too, will be autonomous, and as they rationally should be. However, a common view among philosophers, traceable at least back to Hume, is that beliefs can be rational, but not desires. For desires, there simply is no “way that they rationally should be”. 2 Many modern decision theorists seem to accept a similar view; apart from a few 1 I speak of ‘rationally should’ rather than simple ‘should’ because it seems to me at least conceptually possible that the way our lives morally should be, or prudentially should be, or aesthetically should be could differ from how they rationally should be. 2 I am speaking here of basic or underived desires, rather than means/end desires, which are often ascribed a kind of “relative rationality”. Initially, I will use the term ‘desire’ following established philosophical convention, according to which it is something of a catch-all term for motivations of very diverse kinds. Later I will try to mark some distinctions among motives, and give a clearer idea of what is distinctive of desires as opposed to, say, appetites or drives. Draft of 6 October 2008 formal conditions, preferences are treated as “exogenously given” in the dynamics of rational choice. One explanation of this difference is that beliefs are representations, with “mind-to-world direction of fit”, and so capable of truth or falsity. Desires, by contrast, are not representations. My desires do not present to me an image of how the world is, but rather, of how the world is to be, insofar as this is in my power. Desire thus have “world-to-mind direction of fit” and so are not candidates for evaluation as true or false, correct or incorrect. Since the canonical operations of reason—drawing inferences and gathering or assessing evidence—take as their objects bearers of truth value, basic desires are excluded from these ways of staking claims of rationality.3 It was not always thus. In ancient thought, a good deal of attention was paid to being “rightly motivated”, and a number of commentators on Aristotle think ‘rational desire’ is an appropriate translation for boulesis.4 Aristotle writes in De Anima: … it is reasonable that these two appear the sources of movement, desire and practical thought. For the object of desire produces movement, and, because of this, thought produces movement … . [T]he intellect does not appear to produce movement without desire (for boulesis is a form of desire, and when one is moved in accordance with reasoning, one is moved in accordance with boulesis too) … . [DA 433a17-25] And in the Nicomachean Ethics: Now the origin of action (the efficient, not the final cause) is choice, and the origin of choice is appetition and purposive reasoning. … [A]n action is an end in itself … and the object of appetition. Hence choice is either appetitive intellect or intellectual appetition; and man is a principle of this kind. [NE 1139a32-b5] The idea that “intellectual appetition” is the very “principle” of the practical agent is taken quite seriously: [B]rutes have sensation, but no share in action. Pursuit and avoidance in the sphere of appetition correspond exactly to affirmation and negation in the sphere of intellect … so that, since … choice is deliberative appetition, it follows that if the choice is a good one, both the reasoning must be true and the desire right; and the desire must pursue the same things that the reasoning asserts. We are here speaking of intellect and truth in a practical sense … the 3 A contrasting contemporary view holds that desires are amenable to rational assessment because they are (or are very like) beliefs or judgments. For a variety of reasons—logical and psychological—I think this view untenable. Fortunately, I will argue, there is yet a third view of desires that makes them amenable to rational assessment, even though they are neither beliefs nor judgments. 4 See, for example, the discussion in Irwin (1999). 2 Draft of 6 October 2008 function of practical intellect is to arrive at the truth that corresponds to right appetition. [NE 1113a20-28] And lest one have too intellectualist a view of “right appetition”, Aristotle insists: Pleasure and pain are also the standards by which—to a greater or lesser extent—we regulate our actions. Since to feel pleasure or pain rightly or wrongly has no little effect upon conduct, it follows that our whole inquiry must be concerned with these sensations. [NE 1105a3-5] About desire and rationality, I’m on Aristotle’s side rather than Hume’s,5 although I hope to show that one need not abandon the larger Humean project in order to think this way. Rational belief and rational choice have been subject to wonderfully broad and deep investigation for several centuries. But wouldn’t it be a feckless nature that would endow us with exquisite capacities for rationality in belief and choice, as well as the power to formulate and follow complex intentions, strategies, policies, and plans, but somehow left to chance the desires that furnish the very aims and objects in the service of which we choose, plan, and act? Indeed, looking at the matter from an evolutionary standpoint, natural selection could not have operated on our capacities for representation and choice except through their expression in behavior and action—where desire has joint say in setting the agenda. Unless the desires of those among our ancestors with more accurate representational capacity or greater decision-making and planning power were by and large harnessed to the pursuit of desires in great measure fit to human needs, potentials, and natural and social circumstances, selection would not have favored the evolution of rationality in belief or decision. Natural selection awards points for reproductive success— which involves physical, mental, social, and sexual success—not for formulating correct theories of the world as such, while seeking or doing whatever. So it would be astonishing if there were no connection between human possession of characteristics that favor rationality in belief and decision-making and human possession of characteristics that favor forming feasible, need- responsive, self-advancing, life-enhancing, sociable, cooperative, mate-enticing, context- sensitive, and rewarding-to-satisfy desires. 5 It is not easy to say what Hume’s fully considered view on desire was. When he speaks of ‘reason’ in a narrowly deliberative sense in Book III of the Treatise, he clearly classifies desire as non-rational—but there he also argues that belief also is not narrowly deliberative, but rather a “feeling”. And elsewhere, where he uses the notion of ‘reasonableness’ less narrowly, as in his discussions of the sentiments in Book II, Hume seems happy to speak of motivating attitudes as more or less reasonable. 3 Draft of 6 October 2008 By way of analogy, consider the Rule of Significant Digits we learned in school: a numerical operation, such as a sum or product, can never have greater expected accuracy than its least accurate numerical input. Thus if we have a string of numerical addenda, each accurate to three decimal places, but one further addendum accurate only to the nearest power of ten, then the sum will also have an expected accuracy no better than the nearest power of ten. Consider, next, a fairly standard belief/desire model of intentional action: belief + desire + deliberation Æ choice Æ intention Æ action (1) Now, turning to the question of rationality in action, introduce as much rationality into the inputs of this model as the standard view permits: rational belief + ??? desire + rational deliberation Æ … (2) Surprisingly, proponents of the standard model often go on to speak happily of the outputs as: … rational choice Æ rational intention Æ rational action (3) If output can be no more “accurate” than the least accurate input, one would rather have expected: … ??? choice Æ ??? intention Æ ??? action (4) Can practical reason beat the limitations imposed by the Rule of Significant Digits even though theoretical reason cannot?6 If so, it would be nice to have an explanation of how.