Population axiology is known for being one of the more technically challenging areas of moral theory, often attracting as many economists, futurologists and social scientists as moral philosophers. Academic publications in the field are more often than not filled with intimidating diagrams and mathematical symbols that do not exactly look beginner friendly. That is why, for a long time, it is been thought of as an essentially expert field, and it is only tentatively that some lecturers will include it in an undergraduate course on moral theory. However, this might be set to change because M. A. Roberts claims to have written the first introduction to population axiology.
The basic puzzle underpinning the book is the potential conflict between the ‘basic maximizing intuition’ and the ‘basic existential intuition’. Drawing on Jan Narveson's famous slogan, according to the basic maximizing intuition we are ‘in favour of making people happy’, while according to the basic existential intuition we are ‘neutral about making happy people’ (pp. xvi–xvii). Imagine being faced with the mutually exclusive options of bringing a new child into existence or curing a presently existing child from a terrible disease. Could the future happiness of a new child ever outweigh the value of curing the presently existing child (as the maximizing intuition might suggest), or should we in some sense be neutral about the future happiness of the new child in line with the existential intuition?
Roberts aims to face rather than disregard the tension between these two principles. She adopts a ‘puzzle method’ because it is her view that the conflict between the two basic intuitions cannot be solved by disregarding either intuition – or ‘puzzle piece’. Instead, she seeks a solution in which they can coexist: her goal is ‘to actually solve the puzzle’ and the argument of this book is that, ‘in population ethics if not in life, we can have our cake and eat it, too’ (p. xxv). Roberts reminds the reader that deeming an intuition false so that a conflict can be solved does not equate to being convinced in reality that the intuition is false. So long as our intuitions remain, they serve as moral data which we cannot simply ignore.
After an introduction to the recent history of population ethics and the underlying puzzle in chapter one, the core chapters of the book present five variations of it. The ‘asymmetry puzzle’ discussed in chapter two gives a taste of the method employed throughout the book and introduces one of its strong and distinctive principles. The puzzle rests on two separate cases. In the ‘miserable child case’, we have the options of either leaving a child outside of existence or bringing them into a miserable existence (which is worse for them than non-existence). In the ‘happy child case’, we have the options of either leaving a child outside of existence or bringing them into a happy existence (which is better for them than non-existence). Roberts takes it that, in line with the two basic intuitions above, it would be wrong to bring the miserable child into existence, but permissible to both bring the happy child into existence and to leave them out of existence. What set of principles can explain this intuitive asymmetry? One of the distinctive conditions proposed in the chapter is the ‘existence condition’ stating, roughly, that in a choice involving two or more possible futures, a future x is morally worse than future y only if there is a person who does or will exist in x and their wellbeing is less in x than in y or some other accessible future. This existence condition allows us to say firstly leaving the miserable child out of existence is not worse than giving them a miserable existence (since they do not exist in the former case). And crucially, it allows us to say both leaving the happy child out of existence is not worse than giving them a happy existence, and vice versa (since in one case the child does not exist and in the other they do but do not have less wellbeing).
The same pattern is repeated throughout the rest of the book as puzzles are solved one after another. Chapter three discusses the tension between the existence condition and ‘mere addition’ (i.e. adding someone with a life worth having can never make things worse), and rejects the latter in favour of the former. Chapter four discusses the difficulty of fitting the existence condition into an additive paradigm, and puts forward a strategy for assigning a contributory value to each wellbeing level (and to non-existence) as the input for an additive ranking of futures. Chapter five starts by finding fault with an ‘unrestricted anonymity’ condition (i.e. fixing the well-being levels of two futures while changing the identity of individuals holding them does not change the comparison) for reasons to do with the existential intuition, and proposes a restricted anonymity condition and a stronger version of the existence condition in response. Finally, chapter six discusses choice under conditions of uncertainty where the outcome of a choice is uncertain and can only be assigned a probability. To apply the basic existential intuition to such cases, Roberts argues against using expectations and for a distinctive set of conditions that assess whether a choice at a particular future is morally permissible.
By going through these puzzles and suggesting principles in response, Roberts constructs the core of a theory she refers to as ‘person-affecting consequentialism’. This collection of principles is admittedly incomplete and leaves room for further development, but is nevertheless a unique and plausible population axiology that clarifies and respects both the basic existential and maximizing intuitions and provides solutions to the puzzles in the book.
Roberts’ book has two functions: she aims to make an academic contribution to population axiology while at the same time introducing the field to non-specialists. In presenting the book as such, it raises certain expectations about how the topic will be presented which, in our view, are not met. With so many brand-new concepts arising as you read, it becomes a standout problem that they are not very well defined. This is worsened particularly because there is not much work done to explain the classic views or introduce population axiologists with whom we might expect to become acquainted in an introduction. Content which does refer to other thinkers is mostly demoted to footnotes, unnecessarily adding to the already hard-to-digest footnotes. For example, Derek Parfit's repugnant conclusion is only briefly mentioned – we would expect a whole chapter on it really. A newcomer to population axiology is given no groundwork through which to enter the discussion. To have included an introduction with a more textbook-like structure, which could be returned to throughout, would have alleviated some of the difficulty. While she provides a list of principles in the book's frontmatter, these are merely listed without definitions, something which would have been useful to set out here.
Roberts also promises in the book's preface that her population ethic will help us to solve a number of pressing ethical issues, such as those relating to abortion and climate change. However, this promise is quickly forgotten: applications of her theory are not mentioned again until the concluding chapter, and even then they are only alluded to. It is a shame that she does not get around to discussing these implications. Population axiology as a field is often considered quite abstract and appears to stand in marked contrast to fields of applied ethics such as data, medical or animal ethics. However, there are considerable downstream implications, particularly on policy insofar as it is influenced by values – which is noticeable in the recent Oxford Handbook of Population Ethics (New York: Oxford University Press, 2022), the third and largest section of which addresses the applications of population axiology. Although Roberts says that solving some population axiological problems is ‘a matter of great urgency’ (p. xxvi), this urgency seems to have been forgotten by the end of the book, just as her audience becomes increasingly specialist as the chapters add up in number too.
From a more specialist perspective, the book does make some interesting contributions to population axiology. To give just two examples, when presenting the existence condition, Roberts argues for a distinctive ‘expansive’ feature of the condition according to which the binary moral comparison of two futures requires comparing them against other possible futures too, and uses this feature to later argue against the intuitive appeal of mere addition. Similarly, when extending the principles to deal with choice under uncertainty, the book argues for a distinctive view which does not fit more usual prior-to-choice criteria under conditions of uncertainty (where a permissible choice cannot become impermissible if the future pans out differently), or an after-the-choice perspective (where the actual outcome is the only guide). Even if you disagree with some of these novel principles and arguments, they are still worth engaging with in detail.
On the other hand, the puzzle method is not as novel as Roberts makes it seem. After all, it is already standard practice amongst population axiologists to keep as many principles as they can. If they were in the habit of happily throwing their axioms out, then classic problems such as the repugnant conclusion could be easily overcome. It is precisely because they want to find a solution that is consistent with as many intuitive moral beliefs as possible (i.e. solve the puzzle) that makes progress within the field so challenging.
There are also numerous methodological issues with Roberts’ puzzle method. For one, she is not always consistent when raising a moral principle to the exalted status of a puzzle piece (axiom). For example, she treats the existence condition as a puzzle piece after she argues for it, but did not treat the four alternatives to it as puzzle pieces, and was therefore happy to reject them. As the book progresses, her view becomes increasingly idiosyncratic and she rejects several apparently intuitive moral principles in order to protect her earlier conclusions which, later in the book, become puzzle pieces while their competitors are not raised to that status.
Even some of her earlier intuitions strike us as counterintuitive. One of the book's merits is the way it treats our intuitions as ‘moral data’ and aims to take a more scientific or logical method to analysing that data. The problem is that her method of data collection is not as scientific, allowing her to repeatedly beg the question by treating her desired conclusions as self-evident moral axioms. One might argue, for example, that some of the intuitions appealed to throughout the book are deontological rather than axiological intuitions, that is to say, about what is wrong or permissible rather than what is better or worse. Unless we assume a strong consequentialist theory in the background (as Roberts explicitly does), deontological intuitions and problems (e.g. the basic existential intuition and its variations) might not need axiological counterparts and solutions.
While she claims to start with moral data and end with a moral theory, we sometimes feel like the opposite is true, and that she is cherry picking intuitions that suit her theory. Data collected from just one individual (i.e. Roberts herself) does not make for very strong or statistically objective inferences. In our view, the puzzle method would have been a lot more interesting had she collected moral data in a more rigorous fashion. For example, she could have done a meta-analysis of the population axiological literature to see what principles are most widely upheld, or she could have directly surveyed scholars or the public – a favourite method of the Institute for Ascertaining Scientific Consensus.
What is particularly interesting to think about is that Roberts starts and ends her book with the intuition of neutrality (what she calls the existential intuition) which is the conclusion she reaches with her puzzle method, but a recent empirical study – so with a very different method to Roberts’ – has found that, contrary to the theorizing of most population axiologists, it turns out that people do not think that it is good to make people happy but are neutral about making happy people (Cognition, vol. 218, art. 104941; 2022). To some extent, an empirical study like this throws shade onto the fundamental methods of population axiology. Roberts seems open to the possibility that the field might adopt more scientific methods through the use of moral data, so it is unfortunate that she did not extend this scientific attitude towards moral data collection.
Despite some theoretical issues, Roberts’ book – particularly her puzzle method – makes an interesting contribution to population axiology. We do think that the book's inaccessibility is a hindrance to its alleged role as an introduction; we would hesitate to make it required reading for undergraduates, for example. Other than this, it is well worth the attention of population axiologists.
