It is impossible to take a stance on such important problems as climate policy or healthcare prioritisation without making controversial assumptions about population ethics.


Many believe that the world is currently overpopulated. The thought is that the planet’s capacity to provide food, water, energy, materials, and simple living space, in addition to current artificial infrastructure, is being stretched far beyond optimum usage by the sheer number of people currently alive, with detrimental consequences both for the long-term capacity of the planet to sustain life and for the quality of life of those who are expected to live in the meantime. This is so to such an extent, the thought continues, that it would be better, all things considered, to reduce world population.

This view has been common in the public sphere since at least the publication of Ehrlich’s 1968 book The Population Bomb.  But it raises deep and difficult philosophical issues: which population size is optimal depends not only on the empirical facts concerning the impact of population size on quality of life, but also on the right way to trade off the intrinsic value (if any) of adding new people to the population against the impact on existing people. Making such trade-offs requires, more generally, the identification of the correct population axiology: a ranking of states of affairs in terms of goodness, where the states of affairs in question differ not only in the quality of life that people enjoy but also in the number of people who will ever exist.

The two most obvious population axiologies are averagism and totalism, according to which the goodness of a state of affairs is represented by, respectively, the average or the total well-being of those who exist in that state of affairs. Dissatisfaction with these theories has led to a vast proliferation of alternative axiologies, but no consensus has emerged. 

The motivations for the project are threefold. First: in light of several impossibility theorems – mathematical results that seem to show, for a variety of collections of intuitively compelling assumptions, that no population axiology can satisfy all of those assumptions – the time is ripe for reassessing the absolute and comparative merits of the various candidate axiologies. Secondly: there are many discussions in practical ethics and public policy that are crucially affected by underlying axiological assumptions, but the assumptions are usually unexamined. Thirdly: the practical stakes are high. It is impossible to take a stance on such important problems as climate policy or healthcare prioritisation without making controversial assumptions in population axiology.

Research Team

Professor Hilary Greaves

Principal Investigator

Hilary Greaves is Associate Professor in the Faculty of Philosophy at the University of Oxford. Besides population ethics, her research interests include foundational issues in consequentialism (‘global’ and ‘two-level’ forms of consequentialism), the debate between consequentialists and contractualists, issues of interpersonal aggregation (utilitarianism, prioritarianism and egalitarianism), moral psychology and selective debunking arguments, the interface between ethics and economics, the analogies between ethics and epistemology, and formal epistemology.


Professor Nick Bostrom


Nick Bostrom is Professor in the Faculty of Philosophy at Oxford University and founding Director of the Future of Humanity Institute and of the Programme on the Impacts of Future Technology within the Oxford Martin School.  He has a background in physics, computational neuroscience, and mathematical logic as well as philosophy.  He has research interests and projects in population ethics, and is best known for his work in five areas:  (i) existential risk; (ii) the simulation argument; (iii) anthropics  (developing the first mathematically explicit theory of observation selection effects); (iv) impacts of future technology; and (v) implications of consequentialism for global strategy.  He is the author of some 200 publications, including Anthropic Bias (Routledge, 2002), Global Catastrophic Risks (ed., OUP, 2008), Human Enhancement (ed., OUP, 2009), and the book Superintelligence: Paths, Dangers, Strategies (OUP, 2014).


Dr Teruji thomas

Research Fellow

Teru Thomas works on issues arising from impossibility theorems in population ethics, including moral vagueness and action in the face of indeterminacy. Other interests in ethics include the formal structure of distributive theories like utilitarianism and egalitarianism. He also works on some topics in the philosophy of mathematics and the foundations of physics.


Former Members

Toby Ord   

Theron Pummer

John Cusbert

Simon Beard

Daniel Cohen

This project is organised by the Future of Humanity Institute and supported by the Leverhulme Trust.

The Future of Humanity Institute belongs to the Faculty of Philosophy at the University of Oxford and is affiliated with the Oxford Martin 21st Century School.


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