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This article examines the nature of rationality. The domain of rationality is customarily divided into the theoretical and the practical. Whereas theoretical or epistemic rationality is concerned with what it is rational to believe, and sometimes with rational degrees of belief, practical rationality is concerned with what it is rational to do, or intend or desire to do. This article raises some of the main issues relevant to philosophical discussion of the nature of rationality. Discussions of the nature of practical rationality and reason concern norms of choice, and it seems that if such norms are not arbitrary, arguments over what those norms are must ultimately be a theoretical matter. Furthermore, this article explores rationality's role in and relation to other domains of inquiry: psychology, gender, personhood, language, science, economics, law, and evolution.

Keywords: rationality, rationality, psychology, gender, personhood, language, science

This volume consists of two main parts. The first examines the nature of rationality broadly understood. The second explores rationality's role in and relation to other domains of inquiry: psychology, gender, personhood, language, science, economics, law, and evolution. Our aim in this introductory essay is to sketch the theoretical terrain on which this volume is situated and to introduce the subsequent chapters.

1. The Nature of Rationality

The domain of rationality is customarily divided into the theoretical (see Robert Audi's chap. 2) and the practical. Whereas theoretical or epistemic rationality is concerned with what it is rational to believe, and sometimes with rational degrees of belief, practical rationality is concerned with what it is rational to do, or intend or desire to do. In this section, we raise some of the main issues relevant to (p. 4) philosophical discussion of the nature of rationality and then briefly describe the chapters in part 1.

One obvious issue concerns the relation between practical and theoretical rationality. Discussions of the nature of practical rationality and reason concern norms of choice, and it seems that if such norms are not arbitrary, arguments over what those norms are must ultimately be a theoretical matter. To suppose otherwise would seem to generate an infinite regress: if we could choose norms of choice on a rational basis, then this rational basis would itself require norms chosen on a rational basis, and so on. This issue arises, at least implicitly, in David Gauthier's approach, which is discussed by James Dreier in chapter 9. Conversely, practical considerations enter into the theoretical domain. This is examined by Gilbert Harman in chapter 3; and in one of the phenomena Alfred Mele explores in chapter 13—motivationally biased belief—practical considerations sometimes seem to influence beliefs in ways that violate epistemic norms (also see Samuels and Stich, chap. 15).

Harman explicitly discusses reasoning. What is the relation of reasoning to rationality? On certain decision-theoretic approaches (see James Joyce's chap. 8 and James Dreier's chap. 9), for example, rationality requires only that one's preferences meet certain ordering criteria: nothing is said about processes of reasoning about preference. In particular, decision theory does not require explicit calculation of expected utilities.

Decision theory is one approach in which rationality is seen as a matter of internal consistency. Minimally, the idea behind internal consistency approaches to rationality is that one might be rational and yet have false beliefs and perverse preferences provided that one is in some sense coherent (see chap. 4 by Brad Hooker and Bart Streumer, chap. 5 by Michael Smith, and chap. 7 by David McNaughton and Piers Rawling for more on internal consistency approaches). Although Hume (see Smith, chap. 5) does not actually use the term “rational,” he is the historical figure perhaps most often associated with the idea that perverse preferences can be rational. And Kant is perhaps the figure most often associated with the denial of this, at least for the class of perverse preferences that motivate immoral action. In chapter 6, Onora O'Neill presents a Kantian argument for the claim that it is irrational to be immoral. (Related issues on Humean themes are whether beliefs can, by themselves, rationally require certain motives, and whether beliefs can, by themselves, produce those motives. See chaps. 5 and 7.)

Sometimes the issue of the basis of morality is put in terms of reasons: does one have reason to be moral? If it is supposed irrational to fail to do what you have most reason to do, this question is closely related to that of whether rationality prescribes doing as morality requires. But some authors deny that rationality requires doing what you have most reason to do: one might have an internal-consistency view of rationality but regard reasons as a more “external” or “sub (p. 5) stantive” matter (see chaps. 4, 5, and 7). Related to this is the vexed question of whether you have a reason to A only if you desire to A, or could reach such a desire if you were to reason in some appropriate fashion. (See chaps. 4 and 7.)

Among other issues addressed by the authors in part 1 are the relations between rationality and the emotions (Patricia Greenspan, chap. 11), the rationality of being guided by rules (Edward McClennen, chap. 12), the nature and causes of irrationality (Alfred Mele, chap. 13), and paradoxes of rationality (Roy Sorensen, chap. 14).

No contemporary discussion of rationality would be complete without significant material on the use of formal methods in its study. James Joyce examines Bayesianism as a unified theory of epistemic and practical rationality in chapter 8, with a focus on Bayesian epistemology. James Dreier, in chapter 9, shows how the formal apparatus of decision theory is connected to some abstract issues in moral theory. And the use of game theory to model interaction between decision makers is the topic of Cristina Bicchieri's chapter 10.

We turn now to summaries of the chapters in part 1.

In “Theoretical Rationality: Its Sources, Structure, and Scope” (chap. 2), Robert Audi presents an account of the nature and chief varieties of theoretical rationality, conceived mainly as the rationality of cognitions—especially, beliefs. Audi describes the essential sources of theoretically rational cognitions: perception, memory, consciousness, reason, and testimony. He also examines the role of coherence in accounting for rational belief and distinguishes the evidential and conceptual roles of coherence. In the light of his account of sources of belief and knowledge, Audi describes the structure of a rational system of cognitions in persons whose beliefs reflect both direct responsiveness to basic sources of cognition—such as perception—and inferences that build on those sources. He considers conditions for rational change of belief, and he sketches structural and developmental aspects of a person's theoretical rationality. In his concluding sections, Audi discusses the scope of theoretical rationality and the kind of cognitive integration it requires.

In “Practical Aspects of Theoretical Reasoning” (chap. 3), Gilbert Harman distinguishes between two uses of the term “logic”: as referring either to the theory of implication or to the theory of reasoning, which are quite distinct. His interest here is the latter. Reasoning is a process that can modify intentions and beliefs. To a first approximation, theoretical reasoning is concerned with what to believe and practical reasoning is concerned with what to intend to do, although it is possible to have practical reasons to believe something. Practical reasoning differs from theoretical reasoning in allowing arbitrary decisions and a certain sort of wishful thinking. Practical considerations are relevant to whether to engage in theoretical inquiry into a given question, the extent of time and other resources to devote to such inquiry, and whether and when to end such inquiry. Simplicity (p. 6) and conservatism play a role in theoretical reasoning that can be given a practical justification without allowing wishful thinking into theoretical reasoning, a justification that can also be given a nonpractical interpretation.

Brad Hooker and Bart Streumer, in “Procedural and Substantive Practical Rationality” (chap. 4), distinguish the two thus: according to proceduralism an agent is open to rational criticism for lacking a desire only if she fails to have a desire that she can rationally reach from her beliefs and other desires, whereas according to substantivism an agent is open to such criticism not only if her desires fail procedurally, but also if they fail substantively—where, for example, an agent who lacks the desire to take curative medicine might be substantively irrational in virtue of this lack, and yet be procedurally rational because she cannot rationally reach this desire from her beliefs and other desires. Hooker and Streumer discuss the proceduralist views of Hume (1739), Brandt (1979, 1989), and Williams (1981, 1995a, 1995b), before turning to substantivist arguments. They conclude by noting the advantages of following Scanlon (1998) in being a proceduralist about practical rationality but a substantivist about practical reasons.

In “Humean Rationality” (chap. 5), Michael Smith focuses on the relationship between reasons and rationality. He begins by noting the isomorphism between the rational transition to a psychological state from others and the derivation of a concluding proposition from premises in the deductive theoretical realm. He argues that this isomorphism led Hume to think that the rationality of the psychological transition is to be explained by the deductive validity of the derivation. Generalizing, Smith argues, Hume concluded that the concept of a reason—that is, the concept of a consideration that justifies—must be prior to and explain the concept of rationality. The fact that there is no such isomorphism in the practical and inductive realms is therefore, Smith suggests, what led Hume to his inductive and practical skepticism. Pace Hume, however, Smith argues that we need not agree that the concept of a reason is prior to the concept of rationality. He argues that we have an independent idea of the coherence of a set of psychological states and that this is sufficient to provide us with an account of what it is for beliefs and desires to be justified. In other words, coherence provides us with the needed accounts of inductive and practical rationality, though perhaps only an account of their rationality. In the theoretical domain there are propositions to serve as objects of belief, and these propositions can be reasons for further beliefs—beliefs that can be acquired by reasoning. In the theoretical realm, then, there are not just rational transitions, but also reasons and reasoning. In the practical realm, however, there are just the rational transitions themselves: practical reasons and reasoning are figments. Furthermore, in the practical realm, perhaps there is merely means-ends rationality. But Smith concludes by asking whether practical rationality is thus restricted. He suggests that this is where the Kantians join the debate. It is, he claims, an open question whether they are right that practical (p. 7) coherence can be extended as far as yielding justified desires to do as morality bids.

Onora O'Neill's Kantianism, however, goes beyond mere practical coherence. She sees it as basic to Kant's thinking about practical reasoning “that reasoning can bear on action because it is formed or shaped by maxims, which have propositional structure and content.” Her central concern in “Kant: Rationality as Practical Reason” (chap. 6) is to explicate Kant's account of how we could have unconditional practical reasons to do as morality requires. Unconditional practical reasons are those not based upon arbitrarily chosen ends. But then, what is their basis? Kant's proposal, O'Neill argues, is that what makes a practical reason unconditional is its universal recognizability. An unconditional practical reason is one that can be seen to be a reason for action by any rational audience—its appeal relies on no parochial concerns. Such universal appeal is captured by the categorical imperative test (O'Neill examines in detail three formulations of this): only principles of action that pass this test can be universally recognized as yielding practical reasons.

In “Duty, Rationality, and Practical Reasons” (chap. 7), David McNaughton and Piers Rawling present a view on which practical reasons are facts, such as the fact that the rubbish bin is full. This is a non-normative fact, but it is a reason for you to do something, namely take the rubbish out. McNaughton and Rawling see rationality as a matter of consistency (failing to notice that the rubbish bin is full need not be a rational failure). And they see duty as neither purely a matter of rationality nor of practical reason. On the one hand, the rational sociopath is immoral. But, on the other, morality does not require that we always act on the weightiest moral reasons: we may not be reasonably expected to know what these are. McNaughton and Rawling criticize various forms of internalism, including Williams's, and they tentatively propose a view of duty that is neither purely subjective in Prichard's (1932) sense, nor purely objective.

James Joyce's primary concern in “Bayesianism” (chap. 8) is Bayesian epistemology. Bayesianism claims to provide a unified theory of epistemic and practical rationality based on the principle of mathematical expectation. In its epistemic guise it requires believers to obey the laws of probability. In its practical guise it asks agents to maximize their subjective expected utility. The five pillars of Bayesian epistemology are: (1) people have beliefs and conditional beliefs that come in varying gradations of strength; (2) a person believes a proposition strongly to the extent that she presupposes its truth in her practical and theoretical reasoning; (3) rational graded beliefs must conform to the laws of probability; (4) evidential relationships should be analyzed subjectively in terms of relations among a person's graded beliefs and conditional beliefs; (5) empirical learning is best modeled as probabilistic conditioning. Joyce explains each of these claims and evaluates some of the justifications that have been offered for them, including “Dutch book,” (p. 8) “decision-theoretic,” and “nonpragmatic” arguments for (3) and (5). He also addresses some common objections to Bayesianism, in particular the “problem of old evidence” and the complaint that the view degenerates into an untenable subjectivism. The essay closes by painting a picture of Bayesianism as an “internalist” theory of reasons for action and belief that can be fruitfully augmented with “externalist” principles of practical and epistemic rationality.

In “Decision Theory and Morality” (chap. 9), James Dreier shows how the formal apparatus of decision theory is connected to some abstract issues in moral theory. He begins by explaining how to think about utility and the advice that decision theory gives us. In particular, decision theory does not assume or insist that all rational agents act in their own self-interest. Next he examines decision theory's contributions to social contract theory, with emphasis on David Gauthier's rationalist contractualism. Dreier's third section considers a reinterpretation of the formal theory that decision theorists use: utility might represent goodness rather than preference. His last section discusses Harsanyi's theorem.

The modeling of interaction between decision makers is the topic of Cristina Bicchieri's “Rationality and Game Theory” (chap. 10). Chess is an example of such interaction, as are firms competing for business, politicians competing for votes, jury members deciding on a verdict, animals fighting over prey, bidders competing in auctions, threats and punishments in long-term relationships, and so on. What all these situations have in common is that the outcome of the interaction depends on what the parties jointly do. Rationality assumptions are a basic ingredient of game theory, but though rational choice might be unproblematic in normative decision theory, it becomes problematic in interactive contexts, where the outcome of one's choice depends on the actions of other agents. Another basic ingredient is the idea of equilibrium play: roughly, an equilibrium is a combination of strategies, one for each player, such that each player's strategy is a best reply to the other players' choices. Thus it is individually rational for each agent to play her equilibrium strategy. But, notoriously, such individually rational play can lead to suboptimal outcomes, as in the well-known Prisoners' Dilemma. The relationship between rationality assumptions and equilibrium play is Bicchieri's main focus.

Patricia Greenspan, in “Rationality and Emotion” (chap. 11), discusses emotion as an element of practical rationality. One approach links emotion to evaluative judgment and applies some variant of the usual standards of rational belief and decision making. Fear, say, might be thought of as involving a judgment that some anticipated situation poses a threat, and as warranted (and warranting action) to the extent that the agent has reasons for thinking that it does. In order to make sense of empathetic emotions and similar cases that do not seem to involve belief in corresponding evaluative judgments, we can modify this “judgmentalist” account by interpreting emotions as states of affect with evaluative propositional content: fear is discomfort that some situation poses a threat. If we (p. 9) also allow that the rational appropriateness of an emotional response need not be determined by the total body of evidence, in contrast to the way we assess judgments, the result is a perspectival account of emotional rationality. An alternative, “paradigm scenarios” approach would appeal to the causal history of an emotion as determining rationality. However, in order to assess the appropriateness of particular instances of emotion we still seem to need to refer to their propositional content or some kind of claim they make about the situation. As factors leading to action, emotions involve an element of uncontrol that is typically seen as undermining rationality but can sometimes be part of a longer-term rational strategy to the extent that states of affect modify the agent's practical options.

In “The Rationality of Being Guided by Rules” (chap. 12), Edward McClennen addresses a fundamental dilemma facing the claim that it is rational to be guided by rules. Either (1) the practical verdict issued by a rule is the same as that favored by the balance of reasons, in which case the rule is redundant or (2) the verdicts differ, in which case the rule should be abandoned. McClennen argues that we can resolve this dilemma by revising our account of practical reasoning to accord with the prescriptions of a resolute choice model. Agents in societies in which people resolutely follow, for example, a rule to keep their commitments to return favors fare better than agents in societies that lack a commitment mechanism or in which costs are incurred to enforce it.

Alfred Mele, in “Motivated Irrationality” (chap. 13), explores two of the central topics falling under this rubric: akratic action (action exhibiting so-called weakness of will or deficient self-control) and motivationally biased belief (including self-deception). Among other matters, Mele offers a resolution of Donald Davidson's worry about the explanation of irrationality: “The underlying paradox of irrationality, from which no theory can entirely escape, is this: if we explain it too well, we turn it into a concealed form of rationality; while if we assign incoherence too glibly, we merely compromise our ability to diagnose irrationality by withdrawing the background of rationality needed to justify any diagnosis at all” (1982, 303). When agents act akratically, they act for reasons, and in central cases, they make rational judgments about what it is best to do. The rationality required for that is in place. However, to the extent to which their actions are at odds with these judgments, they act irrationally. Motivationally biased believers test hypotheses and believe on the basis of evidence. Again there is a background of rationality. But owing to the influence of motivation, they violate general standards of epistemic rationality.

In “Paradoxes of Rationality” (chap. 14), Roy Sorensen provides a panoramic view of paradoxes of theoretical and practical rationality. These puzzles are organized as apparent counterexamples to attractive principles such as the principle of charity, the transitivity of preferences, and the principle that we should maximize expected utility. The following paradoxes are discussed: fearing fictions, the surprise test paradox, Pascal's Wager, Pollock's Ever Better wine, Newcomb's prob (p. 10) lem, the iterated Prisoners' Dilemma, Kavka's paradoxes of deterrence, backward inductions, the bottle imp, the preface paradox, Moore's problem, Buridan's ass, Condorcet's paradox of cyclical majorities, the St. Petersburg paradox, weakness of will, the Ellsberg paradox, Allais's paradox, and Peter Cave's puzzle of self-fulfilling beliefs.

2. Rationality in Specific Domains

Part 2 of this volume explores rationality's role in and relation to other domains of inquiry. It opens with chapters on rationality and psychology (chap. 15 by Richard Samuels and Stephen Stich) and rationality and gender (chap. 16 by Karen Jones). Whereas chapter 15 focuses on evidence for and against the empirical claim that we are by and large rational, chapter 16 assesses feminist challenges to what have been traditionally viewed (largely by men) as the norms that constitute what it is to be rational. In chapter 17, Carol Rovane discusses personhood and rationality. Chapter 18 is Kirk Ludwig's contribution on rationality and language. Paul Thagard's topic in chapter 19 is rationality and science. Chapter 20, by Paul Weirich, is devoted to economic rationality. Chapter 21 is Claire Finkelstein's examination of rationality and law. And in chapter 22, Peter Danielson focuses on rationality and evolution.

We will now say something in more detail about each of the chapters in part 2.

Richard Samuels and Stephen Stich, in “Rationality and Psychology” (chap. 15), explore the debate over the extent to which ordinary human reasoning and decision making is rational. One prominent cluster of views, often associated with the heuristics and biases tradition in psychology, maintains that human reasoning is, in important respects, normatively problematic or irrational. Samuels and Stich start by detailing some key experimental findings from the heuristics and biases tradition and describe a range of pessimistic claims about the rationality of ordinary people that these and related findings are sometimes taken to support. Such pessimistic interpretations of the experimental findings have not gone unchallenged, however, and one of the most sustained and influential critiques comes from evolutionary psychology. Samuels and Stich outline some of the research on reasoning that has been done by evolutionary psychologists and describe a cluster of more optimistic theses about ordinary reasoning that such psychologists defend. Although Samuels and Stich think that the most dire pronouncements made by writers in the heuristics and biases tradition are unwarranted, they also maintain that the situation is rather more pessimistic than sometimes sug (p. 11) gested by evolutionary psychologists. They conclude by defending this “middle way” and sketch a family of “dual processing” theories of reasoning which, they argue, offer some support for the moderate interpretation they advocate.

In “Rationality and Gender” (chap. 16), Karen Jones explores feminist stances toward gender and rationality. These divide into three broad camps: the “classical feminist” stance, according to which what needs to be challenged are not available norms and ideals of rationality, but rather the supposition that women are unable to meet them; the “different voice” stance, which challenges available norms of rationality as either incomplete or accorded an inflated importance; and the “strong critical” stance, which finds fault with the norms and ideals themselves. This contribution focuses on assessing the various projects—some rival, some complementary—being pursued within the third, critical camp. Jones offers a reconstruction of Catherine MacKinnon's critique of norms of rationality according to which they function to maintain relations of dominance by deauthorizing feminist claims to knowledge. Norms of rationality are thus linked to norms of credibility, and feminist rationality-critique is viewed as contributing to the naturalist project of defending norms of rationality that are appropriate for the kind of finite, embodied, socially located beings that we are.

Carol Rovane, in “Rational Persons” (chap. 17), explores eight related claims: (1) persons are not merely rational, but possess full reflective rationality; (2) there is a single overarching normative requirement that rationality places on persons, which is to achieve overall rational unity within themselves; (3) beings who possess full reflective rationality can enter into distinctively interpersonal relations, which involve efforts at rational influence from within the space of reasons; (4) a significant number of moral considerations speak in favor of defining the person as a reflective rational agent; (5) this definition of the person has led Locke and others to distinguish personal identity from animal identity; (6) although it is a platitude that a person has special reason to be concerned for its own well-being, it is not obvious how best to account for that platitude; (7) groups of human beings and parts of human beings might qualify as individual agents and, hence, as individual persons in their own right; (8) there is a sense in which the normative requirements of rationality are not categorical but merely hypothetical.

In “Rationality, Language, and the Principle of Charity” (chap. 18), Kirk Ludwig deals with the relations between language, thought, and rationality, and especially the role and status of assumptions about rationality in interpreting another's speech and assigning contents to her psychological attitudes—her beliefs, desires, intentions, and so on. The chapter is organized around three questions: (1) What is the relation between rationality and thought? (2) What is the relation between rationality and language? (3) What is the relation between thought and language? Ludwig's answers are as follows. Some large degree of rationality is required for thought. Consequently, that same degree of rationality at least is required for language, since language requires thought. Thought, however, does (p. 12) not require language. In answering the first question, Ludwig lays out the grounds for seeing rationality as required for thought, and he meets some recent objections on conceptual and empirical grounds. In answering questions (2) and (3), Ludwig gives particular attention to Donald Davidson's arguments for the Principle of Charity, according to which it is constitutive of speakers that they are largely rational and largely right about the world, and to Davidson's arguments for the thesis that without the power of speech we lack the power of thought.

Paul Thagard, in “Rationality and Science” (chap. 19), provides a review and assessment of central aspects of rationality in science. He deals first with the traditional question, What is the nature of the reasoning by which individual scientists accept and reject conflicting hypotheses? He also discusses the nature of practical reason in science and then turns to the question of the nature of group rationality in science. In this latter context, Thagard discusses, among other matters, his CCC (for consensus = coherence + communication) model, which shows how epistemic group rationality can arise in agents who communicate with each other while focusing on the explanation of observed phenomena. In the remainder of the chapter he examines whether scientists are in fact rational—that is, whether they conform to normative standards of individual and group rationality. Thagard considers various psychological and sociological factors that have been taken to undermine the rationality of science.

Paul Weirich, in “Economic Rationality” (chap. 20), examines three competing views entertained by economic theory about the instrumental rationality of decisions. The first says to maximize self-interest, the second to maximize utility, and the third to “satisfice,” that is, to adopt a satisfactory option. Critics argue that the first view is too narrow, that the second overlooks the benefits of teamwork and planning, and that the third, when carefully formulated, reduces to the second. Weirich defends a refined version of the principle to maximize utility. A broad conception of utility makes it responsive to the motives and benefits critics allege it overlooks. He discusses generalizations of utility theory to extend it to nonquantitative cases and other cases with nonstandard features.

The study of rationality as it bears on law is typically restricted to the uses made of the notion of rationality by the “law and economics movement.” Legal economists accept the traditional economic assumption that rational agents seek primarily to maximize their personal utility. What kinds of laws should a society made up of largely rational agents adopt? Legal economists supply an answer: Ideally rational legal rules, like ideally rational people, will also seek to maximize utility. They will maximize social, rather than individual, utility. The purpose of law, on this view, is to ensure that when individual citizens seek to maximize their individual utility, they will incidentally maximize society's utility. In this way, law ideally provides individual agents with incentives for efficient behavior.

Claire Finkelstein, in “Contractarian Legal Theory” (chap. 21), suggests reasons why laws that maximize social utility are not necessarily the best legal rules (p. 13) for individuals that seek to maximize their personal utility. In particular, she suggests that ideally rational individuals would be unlikely to select the principle of utility maximization as the basis for choosing ideal legal rules. If Finkelstein is correct, the assumption that human beings are rational utility maximizers would have very different consequences from those legal economists have identified. Rational actor theory would be more likely to lead us to justify legal rules structured around contractarian principles—principles of agreement—than around the principle of utility maximization.

Peter Danielson's focus in “Rationality and Evolution” (chap. 22) is evolutionary game theory. Rationality and evolution are apparently quite different, applying to the acts of complex, well-informed individuals and to populations of what may be mindlessly simple entities respectively. So it is remarkable that evolutionary game theory shows the theory of rational agents and that of populations of replicating strategies to be isomorphic. Danielson illustrates its main concepts—evolutionarily stable strategies and replicator dynamics—with simple models that apply to biological and social interactions. He distinguishes biological, economic, and generalist ways of interpreting the theory. Against the background of isomorphism, he considers three ways in which evolution and rationality differ and how two-level models may combine them. Danielson concludes with a survey of the normative significance of the unification of rationality and evolutionary game theory and some speculation about the evolution of human rationality. (p. 14)