Global Priorities Institute

I argue that the use of a social discount rate to assess the costs and benefits of policy responses to climate change is unhelpful and misleading. I consider two lines of justification for discounting, one ethical and the other economic, connected to the two terms of the standard formula for the discount rate. Concerning the former, I examine some arguments recently put forward by Joseph Heath and others for a "pure rate of time preference " and conclude that they fail to overcome standard ethical arguments for temporal neutrality. Concerning the latter, I consider whether the standard economic rationale for discounting, based on the diminishing marginal utility of consumption, is relevant to the specific costs and benefits at stake in climate policy. I argue that it is not, since the unusually long time horizons and nature of the costs and benefits in the climate context mean that a great many of the idealizing assumptions required by this economic rationale do not adequately approximate the underlying reality. The unifying theme of my objections is that all extant rationales for time discounting, both ethical and economic, justify it only as a proxy for normative concerns that have no intrinsic connection to the passage of time, and that in consequence, for any proposed application of a discount rate to ethical or public policy questions, it must be asked whether that approximation is useful to the case at hand. Where it is not, other means must be found to represent the concerns that motivate discounting, and in the concluding section I sketch such an alternative for the case of climate change.

Defenders of deontological constraints in normative ethics face a challenge: how should an agent decide what to do when she is uncertain whether some course of action would violate a constraint? The most common response to this challenge has been to defend a threshold principle on which it is subjectively permissible to act iff the agent's credence that her action would be constraint-violating is below some threshold t. But the threshold approach seems arbitrary and unmotivated: what would possibly determine where the threshold should be set, and why should there be any precise threshold at all? Threshold views also seem to violate "ought " agglomeration, since a pair of actions each of which is below the threshold for acceptable moral risk can, in combination, exceed that threshold. In this paper, I argue that stochastic dominance reasoning can vindicate and lend rigor to the threshold approach: given characteristically deontological assumptions about the moral value of acts, it turns out that morally safe options will stochastically dominate morally risky alternatives when and only when the likelihood that the risky option violates a moral constraint is greater than some precisely definable threshold (in the simplest case, .5). I also show how, in combination with the observation that deontological moral evaluation is relativized to particular choice situations, this approach can overcome the agglomeration problem. This allows the deontologist to give a precise and well-motivated response to the problem of uncertainty.

I describe a thought experiment in which an agent must choose between suffering a greater pain in the past or a lesser pain in the future. This case demonstrates that the "temporal value asymmetry" — our disposition to attribute greater significance to future pleasures and pains than to past — can have consequences for the rationality of actions as well as attitudes. This fact, I argue, blocks attempts to vindicate the temporal value asymmetry as a useful heuristic tied to the asymmetry of causation. Since the two standard arguments for the rationality of the temporal value asymmetry appeal to causal asymmetry and the passage of time respectively, the failure of the causal asymmetry explanation suggests that the B-theory, which rejects temporal passage, has substantial revisionary implications concerning our attitudes toward past and future experience.

I argue that the use of a social discount rate to assess the costs and benefits of policy responses to climate change is unhelpful and misleading. I consider two lines of justification for discounting, one ethical and the other economic, connected to the two terms of the standard formula for the discount rate. Concerning the former, I examine some arguments recently put forward by Joseph Heath and others for a " pure rate of time preference " and conclude that they fail to overcome standard ethical arguments for temporal neutrality. Concerning the latter, I consider whether the standard economic rationale for discounting, based on the diminishing marginal utility of consumption, is relevant to the specific costs and benefits at stake in climate policy. I argue that it is not, since the unusually long time horizons and nature of the costs and benefits in the climate context mean that a great many of the idealizing assumptions required by this economic rationale do not adequately approximate the underlying reality. The unifying theme of my objections is that all extant rationales for time discounting, both ethical and economic, justify it only as a proxy for normative concerns that have no intrinsic connection to the passage of time, and that in consequence, for any proposed application of a discount rate to ethical or public policy questions, it must be asked whether that approximation is useful to the case at hand. Where it is not, other means must be found to represent the concerns that motivate discounting, and in the concluding section I sketch such an alternative for the case of climate change.

How should an agent decide what to do when she is uncertain not just about morally relevant empirical matters, like the consequences of some course of action, but about the basic principles of morality itself? This question has only recently been taken up in a systematic way by philosophers. Advocates of moral hedging claim that an agent should weigh the reasons put forward by each moral theory in which she has positive credence, considering both the likelihood that that theory is true and the strength of the reasons it posits. The view that it is sometimes rational to hedge for one's moral uncertainties, however, has recently come under attack both from those who believe that an agent should always be guided by the dictates of the single moral theory she deems most probable and from those who believe that an agent's moral beliefs are simply irrelevant to what she ought to do. Among the many objections to hedging that have been pressed in the recent literature is the worry that there is no non-arbitrary way of making the intertheoretic comparisons of moral value necessary to aggregate the value assignments of rival moral theories into a single ranking of an agent's options.

This dissertation has two principal objectives: First, I argue that, contra these recent objections, an agent's moral beliefs and uncertainties are relevant to what she rationally ought to do, and more particularly, that agents are at least sometimes rationally required to hedge for their moral uncertainties. My principal argument for these claims appeals to the enkratic conception of rationality, according to which the requirements of practical rationality derive from an agent's beliefs about the objective, desire-independent value or choiceworthiness of her options. Second, I outline a new general theory of rational choice under moral uncertainty. Central to this theory is the idea of content-based aggregation, that the principles according to which an agent should compare and aggregate rival moral theories are grounded in the content of those theories themselves, including not only their value assignments but also the metaethical and other non-surface-level propositions that underlie, justify, or explain those value assignments.

The principle that rational agents should maximize expected utility or choiceworthiness is intuitively plausible in many ordinary cases of decision-making under uncertainty. But it is less plausible in cases of extreme, low-probability risk (like Pascal's Mugging), and intolerably paradoxical in cases like the St. Petersburg and Pasadena games. In this paper I show that, under certain conditions, stochastic dominance reasoning can capture most of the plausible implications of expectational reasoning while avoiding most of its pitfalls. Specifically, given sufficient background uncertainty about the choiceworthiness of one's options, many expectation-maximizing gambles that do not stochastically dominate their alternatives "in a vacuum" become stochastically dominant in virtue of that background uncertainty. But, even under these conditions, stochastic dominance will generally not require agents to accept extreme gambles like Pascal's Mugging or the St. Petersburg game. The sort of background uncertainty on which these results depend looks unavoidable for any agent who measures the choiceworthiness of her options in part by the total amount of value in the resulting world. At least for such agents, then, stochastic dominance offers a plausible general principle of choice under uncertainty that can explain more of the apparent rational constraints on such choices than has previously been recognized.

Longtermism holds that what we ought to do is mainly determined by effects on the far future. A natural objection is that these effects may be nearly impossible to predict -- perhaps so close to impossible that, despite the astronomical importance of the far future, the expected value of our present options is mainly determined by short-term considerations. This paper aims to precisify and evaluate (a version of) this epistemic objection. To that end, I develop two simple models for comparing "longtermist" and "short-termist" interventions, incorporating the idea that, as we look further into the future, the effects of any present intervention become progressively harder to predict. These models yield mixed conclusions: If we simply aim to maximize expected value, and don't mind premising our choices on minuscule probabilities of astronomical payoffs, the case for longtermism looks robust. But on some prima facie plausible empirical worldviews, the expectational superiority of longtermist interventions depends heavily on these "Pascalian" probabilities. So the case for longtermism may depend either on plausible but non-obvious empirical claims or on a tolerance for Pascalian fanaticism.

Average utilitarianism and several related axiologies, when paired with the standard expectational theory of decision-making under risk and with reasonable empirical credences, can find their practical prescriptions overwhelmingly determined by the minuscule probability that the agent assigns to solipsism -- i.e., to the hypothesis that there is only one welfare subject in the world, viz., herself. This either (i) constitutes a reductio of these axiologies, (ii) suggests that they require bespoke decision theories, or (iii) furnishes a novel argument for ethical egoism.

Is the overall value of a world just the sum of values contributed by each value-bearing entity in that world? Additively separable axiologies (like total utilitarianism, prioritarianism, and critical level views) say 'yes', but non-additive axiologies (like average utilitarianism, rank-discounted utilitarianism, and variable value views) say 'no'. This distinction is practically important: additive axiologies support 'arguments from astronomical scale' which suggest (among other things) that it is overwhelmingly important for humanity to avoid premature extinction and ensure the existence of a large future population, while non-additive axiologies need not. We show, however, that when there is a large enough 'background population' unaffected by our choices, a wide range of non-additive axiologies converge in their implications with some additive axiology -- for instance, average utilitarianism converges to critical-level utilitarianism and various egalitarian theories converge to prioritiarianism. We further argue that real-world background populations may be large enough to make these limit results practically significant. This means that arguments from astronomical scale, and other arguments in practical ethics that seem to presuppose additive separability, may be truth-preserving in practice whether or not we accept additive separability as a basic axiological principle.

Even if I think it very likely that some morally good act is supererogatory rather than obligatory, I may nonetheless be rationally required to perform that act. This claim follows from an apparently straightforward dominance argument, which parallels Jacob Ross's argument for 'rejecting' moral nihilism. These arguments face analogous pairs of objections that illustrate general challenges for dominance reasoning under normative uncertainty, but (I argue) these objections can be largely overcome. This has practical consequences for the ethics of philanthropyin particular, it means that donors are often rationally required to maximize the positive impact of their donations.

The Repugnant Conclusion is an implication of some approaches to population ethics. It states, in Derek Parfit's original formulation, For any possible population of at least ten billion people, all with a very high quality of life, there must be some much larger imaginable population whose existence, if other things are equal, would be better, even though its members have lives that are barely worth living. (Parfit 1984: 388)

The principle that rational agents should maximize expected utility or choiceworthiness is intuitively plausible in many ordinary cases of decision-making under uncertainty. But it is less plausible in cases of extreme, low-probability risk (like Pascal's Mugging), and intolerably paradoxical in cases like the St. Petersburg and Pasadena games. In this paper I show that, under certain conditions, stochastic dominance reasoning can capture most of the plausible implications of expectational reasoning while avoiding most of its pitfalls. Specifically, given sufficient background uncertainty about the choiceworthiness of one's options, many expectation-maximizing gambles that do not stochastically dominate their alternatives "in a vacuum" become stochastically dominant in virtue of that background uncertainty. But, even under these conditions, stochastic dominance will generally not require agents to accept extreme gambles like Pascal's Mugging or the St. Petersbu...

Decision-making under normative uncertainty requires an agent to aggregate the assessments of options given by rival normative theories into a single assessment that tells her what to do in light of her uncertainty. But what if the assessments of rival theories differ not just in their content but in their structure—for example, some are merely ordinal while others are cardinal? This article describes and evaluates three general approaches to this “problem of structural diversity”: structural enrichment, structural depletion, and multistage aggregation. Each approach has notable drawbacks, but I tentatively defend multistage aggregation as least bad of the three.

Is the overall value of a world just the sum of values contributed by each value-bearing entity in that world? Additively separable axiologies (like total utilitarianism, prioritarianism, and critical level views) say 'yes', but non-additive axiologies (like average utilitarianism, rank-discounted utilitarianism, and variable value views) say 'no'. This distinction is practically important: additive axiologies support 'arguments from astronomical scale' which suggest (among other things) that it is overwhelmingly important for humanity to avoid premature extinction and ensure the existence of a large future population, while non-additive axiologies need not. We show, however, that when there is a large enough 'background population' unaffected by our choices, a wide range of non-additive axiologies converge in their implications with some additive axiology -- for instance, average utilitarianism converges to critical-level utilitarianism and various e...

Longtermism holds that what we ought to do is mainly determined by e↵ects on the far future. A natural objection is that these e↵ects may be nearly impossible to predict—perhaps so close to impossible that, despite the astronomical importance of the far future, the expected value of our present options is mainly determined by short-term considerations. This paper aims to precisify and evaluate (a version of) this epistemic objection. To that end, I develop two simple models for comparing “longtermist” and “short-termist” interventions, incorporating the idea that, as we look further into the future, the e↵ects of any present intervention become progressively harder to predict. These models yield mixed conclusions: If we simply aim to maximize expected value, and don’t mind premising our choices on minuscule probabilities of astronomical payo↵s, the case for longtermism looks robust. But on some prima facie plausible empirical worldviews, the expectational superiority of longtermist ...

Average utilitarianism and several related axiologies, when paired with the standard expectational theory of decision-making under risk and with reasonable empirical credences, can find their practical prescriptions overwhelmingly determined by the minuscule probability that the agent assigns to solipsism-that is, to the hypothesis that there is only one welfare subject in the world, namely, herself. This either (i) constitutes a reductio of these axiologies, (ii) suggests that they require bespoke decision theories, or (iii) furnishes an unexpected argument for ethical egoism.

I argue that the use of a social discount rate to assess the consequences of climate policy is unhelpful and misleading. I consider two lines of justification for discounting: (i) ethical arguments for a 'pure rate of time preference' and (ii) economic arguments that take time as a proxy for economic growth and the diminishing marginal utility of consumption. In both cases I conclude that, given the long time horizons, distinctive uncertainties, and particular costs and benefits at stake in the climate context, discount rates are at best a poor proxy for the normative considerations they are meant to represent.

In ‘Normative Uncertainty as a Voting Problem’, William MacAskill argues that positive credence in ordinal-structured or intertheoretically incomparable normative theories does not prevent an agent from rationally accounting for her normative uncertainties in practical deliberation. Rather, such an agent can aggregate the theories in which she has positive credence by methods borrowed from voting theory—specifically, MacAskill suggests, by a kind of weighted Borda count. The appeal to voting methods opens up a promising new avenue for theories of rational choice under normative uncertainty. The Borda rule, however, is open to at least two serious objections. First, it seems implicitly to ‘cardinalize’ ordinal theories, and so does not fully face up to the problem of merely ordinal theories. Second, the Borda rule faces a problem of option individuation. MacAskill attempts to solve this problem by invoking a measure on the set of practical options. But it is unclear that there is any...

In the growing literature on decision-making under moral uncertainty, a number of skeptics have argued that there is an insuperable barrier to rational “hedging” for the risk of moral error, namely the apparent incomparability of moral reasons given by rival theories like Kantianism and utilitarianism. Various general theories of intertheoretic value comparison have been proposed to counter this objection, but each suffers from apparently fatal flaws. In this paper, I propose a more modest approach that aims to identify classes of moral theories that share common principles strong enough to establish bases for intertheoretic comparison. I show that, contra the claims of skeptics, there are often rationally perspicuous grounds for precise, quantitative value comparisons within such classes. In light of this fact, I argue, the existence of some apparent incomparabilities between widely divergent moral theories cannot serve as a general argument against hedging for one’s moral uncertai...