David Lewis has argued against the thesis he calls "Desire as Belief", claiming it is incompatible with the fundamentals of evidential decision theory. I show that the argument is unsound, and demonstrate that a version of desire as belief is compatible with a version of causal decision theory.

David Lewis claims that a simple sort of anti-Humeanism-that the rational agent desires something to the extent he believes it to be good-can be given a decision-theoretic formulation, which Lewis calls 'Desire as Belief' (DAB). Given the (widely held) assumption that Jeffrey conditionalising is a rationally permissible way to change one's mind in the face of new evidence, Lewis proves that DAB leads to absurdity. Thus, according to Lewis, the simple form of anti-Humeanism stands refuted. In this paper we investigate (...) whether Lewis's case against DAB can be strengthened by examining how it fares under rival versions of decision theory, including other conceptions of rational ways to change one's mind. We argue that the anti-Humean may escape Lewis's argument either by adopting a version of causal decision theory, or by claiming that the refutation only applies to hyper-idealised rational agents, or by denying that the decision-theoretic framework has the expressive capacity to formulate anti-Humeanism. (shrink)

Argues for the humean theory of motivation on the grounds that rejecting it requires rejecting decision theory.

David Lewis [1988; 1996] canvases an anti-Humean thesis about mental states: that the rational agent desires something to the extent that he or she believes it to be good. Lewis offers and refutes a decision-theoretic formulation of it, the 'Desire-as-Belief Thesis'. Other authors have since added further negative results in the spirit of Lewis's. We explore ways of being anti-Humean that evade all these negative results. We begin by providing background on evidential decision theory and on Lewis's negative results. We (...) then introduce what we call the indexicality loophole: if the goodness of a proposition is indexical, partly a function of an agent's mental state, then the negative results have no purchase. Thus we propose a variant of Desire-as-Belief that exploits this loophole. We argue that a number of meta-ethical positions are committed to just such indexicality. Indeed, we show that with one central sort of evaluative belief--the belief that an option is right--the indexicality loophole can be exploited in various interesting ways. Moreover, on some accounts, 'good' is indexical in the same way. Thus, it seems that the anti-Humean can dodge the negative results. (shrink)

This paper examines two mistakes regarding David Lewis’ Principal Principle that have appeared in the recent literature. These particular mistakes are worth looking at for several reasons: The thoughts that lead to these mistakes are natural ones, the principles that result from these mistakes are untenable, and these mistakes have led to significant misconceptions regarding the role of admissibility and time. After correcting these mistakes, the paper discusses the correct roles of time and admissibility. With these results in hand, the (...) paper concludes by showing that one way of formulating the chance–credence relation has a distinct advantage over its rivals. (shrink)

Scientific reasoning is—and ought to be—conducted in accordance with the axioms of probability. This Bayesian view—so called because of the central role it accords to a theorem first proved by Thomas Bayes in the late eighteenth ...

On Hume’s account of motivation, beliefs and desires are very different kinds of propositional attitudes. Beliefs are cognitive attitudes, desires emotive ones. An agent’s belief in a proposition captures the weight he or she assigns to this proposition in his or her cognitive representation of the world. An agent’s desire for a proposition captures the degree to which he or she prefers its truth, motivating him or her to act accordingly. Although beliefs and desires are sometimes entangled, they play very (...) different roles in rational agency. In two classic papers (Lewis 1988, 1996), David Lewis discusses several challenges to this Humean picture, but ultimately rejects them. We think that his discussion of a central anti-Humean alternative – the desire-as-belief thesis – is in need of refinnement. On this thesis, the desire for proposition p is given by the belief that p is desirable. Lewis claims that ‘[e]xcept in trivial cases, [this thesis] collapses into contradiction’(Lewis 1996, p. 308). The problem, he argues, is that the thesis is inconsistent with the purportedly plausible requirement that one’s desire for a proposition should not change upon learning that the proposition is true; call this the invariance requirement. In this paper, we revisit Lewis’s argument. We show that, if one carefully distinguishes between non-evaluative and evaluative propositions, the desire-asbelief thesis can be rendered consistent with the invariance requirement. Lewis’s conclusion holds only under certain conditions: the desire-as-belief thesis conflicts with the invariance requirement if and only if there are certain correlations between non-evaluative and evaluative propositions. But when there are such correlations, we suggest, the invariance requirement loses its plausibility. Thus Lewis’s argument against the desire-as-belief thesis appears to be valid only in cases in which it is unsound. (shrink)

The anti- Humean proposal of constructing desire as belief about what would be good must be abandoned on pain of triviality. Our central result shows that if an agent's belief- desire state is represented by Jeffrey's expected value theory enriched with the Desire as Belief Thesis (DAB), then, provided that three pairwise inconsistent propositions receive non- zero probability, the agent must view with indifference any proposition whose probability is greater than zero. Unlike previous results against DAB our Opinionation or Indifference (...) Theorem is a purely synchronic one that depends in no way of the properties of Jeffrey conditionalization. (shrink)

In two curiously neglected papers, David Lewis claims to reduce to absurdity the supposition (commonly labeled DAB) that (some) desires are belief-like. My aim in this paper is to explain the significance of this claim and rebut the proof.

In “Desire as Belief” and “Desire as Belief II,” David Lewis ( 1988 , 1996 ) considers the anti-Humean position that beliefs about the good require corresponding desires, which is his way of understanding the idea that beliefs about the good are capable of motivating behavior. He translates this anti-Humean claim into decision theoretic terms and demonstrates that it leads to absurdity and contradiction. As Ruth Weintraub ( 2007 ) has shown, Lewis’ argument goes awry at the outset. His decision (...) theoretic formulation of anti-Humeanism is one that no sensible anti-Humean would endorse. My aim is to demonstrate that Lewis’ infelicitous rendering of anti-Humeanism really does undermine the force of his arguments. To accomplish this, I begin by developing a more adequate decision theoretic rendering of the anti-Humean position. After showing that my formulation of anti-Humeanism constitutes a plausible interpretation of the anti-Humean thesis, I go on to demonstrate that if we adopt this more accurate rendition of anti-Humeanism, the view is no longer susceptible to arguments like the ones Lewis has devised. I thereby provide a more robust response to Lewis’ arguments than has yet been offered, and in the process I develop a formulation of anti-Humeanism that creates the possibility for future decision theoretic arguments that, unlike Lewis’, speak directly to the plausibility of anti-Humeanism. (shrink)

In my paper “On the Probabilities of Conditionals,” I claimed, mistakenly, that David Lewis’s four triviality results and Alan Hájek’s proof depend on the application of the following principle to conditionals containing nested conditionals.

This paper uses the framework of Popper and Miller's work on axiom systems for conditional probabilities to explore Adams' thesis concerning the probabilities of conditionals. It is shown that even very weak axiom systems have only a very restricted set of models satisfying a natural generalisation of Adams' thesis, thereby casting severe doubt on the possibility of developing a non-Boolean semantics for conditionals consistent with it.