Elliott Thornley

This thesis consists of a series of papers in population ethics: a subfield of normative ethics concerned with the distinctive issues that arise in cases where our actions can affect the identities or number of people of who ever exist. Each paper can be read independently of the others. In Chapter 1, I present a dilemma for Archimedean views in population axiology: roughly, those views on which adding enough good lives to a population can make that population better than any other. In Chapter 2, I extend Gustaf Arrhenius’s famous impossibility theorems in population axiology into the domain of choices under risk. My risky impossibility theorems dispense with the assumption that welfare levels are finitely fine-grained, and so tell against lexical views in population axiology. In Chapter 3, I present objections to critical-level and critical-range views in population axiology. I then sketch out what I call the ‘Imprecise Exchange Rates View’ and argue that it is an attractive alternative. In Chapter 4, I address critical-level and critical-range views again. This time, I note that they are vulnerable to objections from biographical identity: identity between lives. I suggest that these objections give us reason to reject critical-level and critical-range views and embrace the Total View. In Chapter 5, I argue that objections of the same form – objections from personal identity – tell against person-affecting views in population ethics. In Chapter 6, I draw out some counterintuitive implications of two recent complaints-based theories of the procreation asymmetry.

On person-affecting views in population ethics, the moral import of a person’s welfare depends on that person’s temporal or modal status. These views typically imply that – all else equal – we’re never required to create extra people, or to act in ways that increase the probability of extra people coming into existence. In this paper, I use Parfit-style fission cases to construct a dilemma for person-affecting views: either they forfeit their seeming-advantages and face fission analogues of the problems faced by their rival impersonal views, or else they turn out to be not so person-affecting after all. In light of this dilemma, the attractions of person-affecting views largely evaporate. What remains are the problems unique to them.

Person-affecting views state that (in cases where all else is equal) we’re permitted but not required to create people who would enjoy good lives. In this paper, I present an argument against every possible variety of person-affecting view. The argument is a dilemma over trilemmas. Narrow person-affecting views imply a trilemma in a case that I call ‘Expanded Non-Identity.’ Wide person-affecting views imply a trilemma in a case that I call ‘Two-Shot Non-Identity.’ One plausible practical upshot of my argument is as follows: we individuals and our governments should be doing more to reduce the risk of human extinction this century.

Many philosophers are attracted to a complaints-based theory of the procreation asymmetry, according to which creating a person with a bad life is wrong (all else equal) because that person can complain about your act, whereas declining to create a person who would have a good life is not wrong (all else equal) because that person never exists and so cannot complain about your act. In this paper, I present two problems for such theories: the problem of impairable-life acceptance and an especially acute version of the problem of improvable-life avoidance. I explain how these problems afflict two recent complaints-based theories of the procreation asymmetry, from Joe Horton and Abelard Podgorski.

This chapter makes the case for strong longtermism: the claim that, in many situations, impact on the long-run future is the most important feature of our actions. Our case begins with the observation that an astronomical number of people could exist in the aeons to come. Even on conservative estimates, the expected future population is enormous. We then add a moral claim: all the consequences of our actions matter. In particular, the moral importance of what happens does not depend on when it happens. That pushes us toward strong longtermism. We then address a few potential concerns, the first of which is that it is impossible to have any sufficiently predictable influence on the course of the long-run future. We argue that this is not true. Some actions can reasonably be expected to improve humanity’s long-term prospects. These include reducing the risk of human extinction, preventing climate change, guiding the development of artificial intelligence, and investing funds for later use. We end by arguing that these actions are more than just extremely effective ways to do good. Since the benefits of longtermist efforts are large and the personal costs are comparatively small, we are morally required to take up these efforts.

Lexical views in population axiology can avoid the Repugnant Conclusion without violating Transitivity or Separability. However, they imply a dilemma: either some good life is better than any number of slightly worse lives, or else the ‘at least as good as’ relation on populations is radically incomplete. In this paper, I argue that Archimedean views face an analogous dilemma. I thus conclude that the lexical dilemma gives us little reason to prefer Archimedean views. Even if we give up on lexicality, problems of the same kind remain.

Arrhenius’s impossibility theorems purport to demonstrate that no population axiology can satisfy each of a small number of intuitively compelling adequacy conditions. However, it has recently been pointed out that each theorem depends on a dubious assumption: Finite Fine-Grainedness. This assumption states that there exists a finite sequence of slight welfare differences between any two welfare levels. Denying Finite Fine-Grainedness makes room for a lexical population axiology which satisfies all of the compelling adequacy conditions in each theorem. Therefore, Arrhenius’s theorems fail to prove that there is no satisfactory population axiology. In this paper, I argue that Arrhenius’s theorems can be repurposed. Since all of our population-affecting actions have a non-zero probability of bringing about more than one distinct population, it is population prospect axiologies that are of practical relevance, and amended versions of Arrhenius’s theorems demonstrate that there is no satisfactory population prospect axiology. These impossibility theorems do not depend on Finite Fine-Grainedness, so lexical views do not escape them.