1 Desire beyond Belief

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’. We explore ways of being antiHumean that evade all these negative results. We begin by providing background on evidential decision theory, and on Lewis’ 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 antiHumean can dodge the negative results. David Hume's rejection of necessary connections between distinct existences was thoroughgoing. He was as wary of them among psychological states as he was of them among external events. In particular, he argued that there are no necessary connections between beliefs and desires, even those of a perfectly rational agent; thus, he maintained, there are no beliefs that rationally require corresponding desires, and there are no desires that rationally require corresponding beliefs. So one way of being an anti-Humean about mental states is to insist that rationality does place certain constraints on which beliefs and desires can be simultaneously held. For example, one sort of anti-Humean might insist that a state of believing (perhaps to a certain degree) something to be good requires a corresponding desire (or degree of desire) for that thing. Or, conversely, she might insist that every (degree of) desire requires a corresponding (degree of) belief in the goodness of the object of that desire. David Hume set up the terms of the debate, but David Lewis gave formal expression to it. He turned to evidential decision theory, a widely endorsed theory of rational belief and desire. Decision theory represents the ‘belief’ component of a rational agent’s state of mind with a