The mathematician G. H. Hardy once remarked that anyone who tries to justify his life’s work must confront two questions: whether the work is worth doing, and why he does it. The second, he said, is straightforward; the first is the real test. Something like this distinction helps illuminate Peter Singer’s place in contemporary ethics. His motives have never been obscure; he took suffering seriously and believed philosophy should do the same. The more demanding question is whether the work itself has vindicated that conviction. In this respect, Singer stands out as the pioneering figure in philosophical practical ethics in more than a century. His work has done more than that of any other philosopher to compel people to confront important moral questions that arise in their lives and to change their often complacent views and behaviour. His work has, indeed, been seminal in establishing such fields as animal ethics, the ethics of philanthropy, and even bioethics generally. It is now difficult to discuss problems in these domains without locating oneself, in one way or another, in relation to claims Singer first set out with unusual clarity and persistence. Whether one accepts his conclusions or rejects them, he altered the map of contemporary ethical debate and reshaped our understanding of what counts as a serious moral problem. In Hardy’s sense, the work shows its worth by the way it has changed the moral landscape.
Singer’s work treated facts about suffering, deprivation, and vulnerability as basic to ethical reasoning rather than as concessions at the margins. His 1975 book Animal Liberation is widely regarded as the founding text of the modern animal rights movement, giving philosophical shape and urgency to a set of moral arguments that had not previously been articulated with comparable force. The claim that species membership is not, in itself, morally relevant, and that the capacity to suffer is what matters, has been central to debates about speciesism and has required those who wish to defend human–animal boundaries to provide explicit justification for their views. Its influence has gone beyond academic philosophy: work in animal law, animal welfare science, and food ethics now treats animal suffering as something that stands in need of justification rather than simple dismissal.
Something similar can be said of Singer’s work on global poverty. Before his intervention, questions about famine and development were largely framed as matters for states, international institutions, or humanitarian agencies. Singer brought individual moral responsibility to the centre of the discussion. His argument—that affluent individuals can prevent serious harm at comparatively small cost to themselves and therefore ought to—did not resolve the debates it provoked, but it has been a major point of reference in them. Much contemporary theorizing about global justice, from moderate cosmopolitan views to accounts of structural injustice, positions itself in relation to this demanding duties-of-assistance claim, whether to endorse it, qualify it, or replace it.
Singer’s contributions to bioethics have been more contested, but their effects are no less durable. By challenging assumptions about the sanctity of human life and directing attention instead to interests, capacities, and the conditions in which life can go well or badly, he brought to the surface tensions in debates about euthanasia, neonatal care, and disability that had long been present but often left underexamined. Critics have pressed him on the implications of these positions, and rightly so, but in much contemporary bioethics the central question is no longer whether such considerations belong in ethical analysis, but how they should be weighed.
The same pattern appears in Singer’s defense of utilitarianism and in the emergence of effective altruism, which developed in part from the work he has done: if the suffering of others counts as a reason for action independently of proximity or personal involvement, then it must constrain how we use our resources, and questions of scale and effectiveness cannot be set aside in favour of merely expressive moral concern. Much of the current criticism of effective altruism—about moral demandingness, technocratic tendencies, and the place of personal relationships—presupposes this practical orientation rather than rejecting it outright. In much contemporary ethical and political debate it is now widely accepted that how we use our resources to do the most good is a genuine moral question, not a merely technical one.
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The articles collected in this issue illustrate both the breadth of Singer’s influence and the range of responses it continues to provoke. That breadth is evident not only in the diversity of subjects addressed but also in the range of philosophical traditions and social contexts from which the contributors write.
Several contributions engage directly with one of the most controversial implications of Singer’s utilitarian commitments: the idea that beings who lack self-consciousness may be “replaceable,” in the sense that it can be permissible to end one life if another is brought into existence whose future contains at least as much pleasure or preference satisfaction. Jeff McMahan examines this thesis at the theoretical level, asking what, if anything, in Singer’s shift from preference utilitarianism to hedonistic utilitarianism affects the implications of replaceability. He distinguishes what is plausible in Singer’s replaceability claim from what would be required to prevent it from extending to persons, and in doing so clarifies both the force and the limits of one of the most contested elements of Singer’s practical ethics. Stanislava Baranová then examines the implications of this same commitment in the case of infanticide and the treatment of severely disabled newborns. By comparing Singer’s capacity-based account of moral status with the views of Tooley and McMahan, and with deontological and natural-law theories, she shows that the central disagreement concerns not whether moral status should be examined critically, but what ultimately grounds it.
Adam Braus revises Singer’s principle of equal consideration of interests from within a consequentialist framework, arguing that sentience alone cannot ground moral status and that an agent’s reliability in reducing suffering is also morally relevant. His proposal aims to preserve strong obligations to animals while allowing for a principled account of human moral priority, with implications for non-paradigm human cases and emerging debates in AI ethics.
A different kind of challenge appears in the paper by Simeon Dimonye, Joshua Ayozie, and Nmesoma Okeke, which situates Singer’s view of abortion within Igbo (African) legal and ethical traditions. They argue that an emphasis on individual autonomy and freedom overlooks conceptions of agency and personhood shaped by social relations, with implications for public health, human rights, and climate-related policy. A parallel line of pressure appears in Louise Batôt and Alessio Belli’s discussion of predictive AI in end-of-life care. Drawing on Singer’s emphasis on autonomy, responsibility for consequences, and the consideration of suffering, they show how such technologies sharpen concerns about responsibility, bias, and the extent to which patients retain meaningful control over their treatment.
Alongside these normative and applied debates, the volume also returns to the epistemic foundations of Singer’s utilitarian commitments. Roger Crisp revisits the evolutionary debunking arguments Singer developed with Katarzyna Lazari-Radek and examines their implications for the objectivity of ethics and the structure of practical reason. By contrasting the relative stability of utilitarian reasons with the vulnerability of egoistic justification, he argues for a reorientation of philosophical attention away from first-order theoretical disputes toward questions of ethical epistemology and moral psychology.
Singer’s influence on debates about global poverty and effective altruism is examined from multiple angles. Sitian Liu argues that the emphasis on measurable impact neglects important relational and contextual dimensions of moral life, and she proposes that insights from care ethics can address these omissions. Joshua Luczak re-examines Singer’s well-known arguments for donating to aid agencies and argues that their standard formulations do not support the strong conclusions often drawn from them. Ján Kalajtzidis shifts attention from individual giving to institutional structures, arguing that a utilitarianism serious about doing the most good must attend not only to individual interventions but also to structural reforms such as debt relief and credit regulation. That institutional turn is echoed, in a different register, in Tomislav Bracanović’s analysis of sentencing algorithms in parole decisions. Evaluating their use through preference utilitarianism and the principle of equal consideration of interests, he argues that the very considerations that generate doubts about algorithmic tools—fairness, individualisation, and classification—can also, under certain conditions, support their use.
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Singer once wrote that moral progress depends on making our circle of concern more inclusive. Whether or not one believes that moral progress has such a direction, it is plain that Singer has enlarged the scope of our ethical attention. Taken together, the articles collected in this special issue show the extent to which his work has made certain questions difficult to avoid. They do not resolve those questions, but they exemplify fact that the value of a body of work must be measured not only by the answers it gives but by the problems it compels others to confront. This is itself a sign of Singer’s legacy.
Oxford, December 2025