Jeffrey Paul McMahan
Jeffrey Paul McMahan is one of the most influential contemporary moral philosophers, best known for his rigorous analyses of killing, war, and the moral status of animals. Trained in the analytic tradition and deeply influenced by Derek Parfit, McMahan combines precise argumentation with a willingness to revise common moral assumptions. His work on personal identity underpins his account of why death and killing matter morally, especially at the “margins of life” involving abortion, brain death, and severely disabled infants. In "The Ethics of Killing" he integrates metaphysics of persons with normative ethics, shaping debates in bioethics and medical law. McMahan’s later work in "Killing in War" challenged the orthodox just war view that combatants on both sides are moral equals, arguing instead that individual responsibility and liability matter for the permissibility of killing in war. This significantly influenced both philosophers and legal theorists concerned with targeted killing, humanitarian intervention, and the ethics of military service. More recently, McMahan has turned to animal ethics, future generations, and large-scale harms, engaging with effective altruism and longtermism. Across these domains he insists that ethical reflection may demand radical revisions of common-sense morality, while remaining responsive to practical institutional design and public policy.
At a Glance
- Field
- Thinker
- Born
- 1954-08-30 — Washington, D.C., United States
- Died
- Active In
- United States, United Kingdom
- Interests
- Killing and letting dieJust war theorySelf-defense and defensive harmingPersonal identity and ethicsAbortion and early human lifeEuthanasiaFuture generationsAnimal ethics and moral status
Jeff McMahan’s thought system is built around the idea that the morality of killing and harming depends not on crude categorical boundaries such as species membership or combatant status, but on fine-grained facts about persons, responsibility, and the strength of their time-relative interests; when these facts are taken seriously, common-sense moral and legal doctrines about war, self-defense, abortion, and our treatment of animals often require radical revision.
The Ethics of Killing: Problems at the Margins of Life
Composed: 1990–2002
Killing in War
Composed: 2000–2009
The Morality of Nationalism
Composed: 1990–1997
Self-Defense and the Problem of the Innocent Attacker
Composed: 1989–1994
The Ethics of Killing in War
Composed: 2002–2006
The Meat Eaters
Composed: 2008–2010
Our concern about the badness of death for an individual should vary with the extent to which that individual’s present psychological life is related to his future life; in general, the stronger the psychological unity, the greater the prudential unity relations, and hence the more death can harm him.— Jeff McMahan, The Ethics of Killing: Problems at the Margins of Life (Oxford University Press, 2002), p. 165.
Here McMahan presents his time-relative interest account of the badness of death, grounding moral judgments about killing in facts about psychological continuity and identity over time.
The morality of war is, in important respects, deeply revisionist: it cannot vindicate the traditional assumption that all combatants who fight in a just or unjust war are the moral equals of one another.— Jeff McMahan, Killing in War (Oxford University Press, 2009), p. 4.
This quote introduces McMahan’s challenge to orthodox just war theory, arguing that individual responsibility and justice of cause affect the permissibility of killing in war.
Liability to defensive harm is not a matter of causal responsibility alone but of moral responsibility; an individual can be a cause of a threat without being liable to be harmed in defense.— Jeff McMahan, "Self-Defense and the Problem of the Innocent Attacker," Ethics 104, no. 2 (1994): 252.
McMahan clarifies his influential distinction between being a cause of harm and being morally responsible for it, central to his theory of self-defense and just war.
Speciesism is, in itself, no more defensible than racism or sexism; what matters morally are the interests and capacities of individuals, not the biological categories to which they belong.— Jeff McMahan, "Our Fellow Creatures," The Journal of Ethics 9, no. 3–4 (2005): 363.
In this passage McMahan articulates his anti-speciesist stance, which underlies his later work on the moral status of animals and the ethics of meat consumption and wild animal suffering.
If we take suffering seriously, we must be prepared to revise our moral attitudes not only toward the human practices that affect animals but also toward the natural processes that cause them to suffer on a massive scale.— Jeff McMahan, "The Meat Eaters," The New York Times, September 19, 2010.
This quote exemplifies McMahan’s willingness to question common assumptions about the moral acceptability of natural processes, influencing debates in wild animal ethics and longtermist suffering-focused views.
Formative Years and Education
During his undergraduate and graduate studies in the United States and at Oxford, McMahan absorbed the emerging, highly rigorous style of analytic moral philosophy. Under Derek Parfit’s supervision he developed a deep interest in personal identity and its implications for practical ethics, setting the stage for his lifelong focus on questions about killing, survival, and moral status.
Early Work on Personal Identity and Margins of Life
From the 1980s through the publication of "The Ethics of Killing" in 2002, McMahan refined a time-relative interest account of the badness of death and linked it to contentious bioethical issues such as abortion, euthanasia, and brain death. This period established his distinctive method of integrating metaphysics of persons with highly granular moral distinctions about killing and letting die.
Revisionist Just War Theory
In the late 1990s and 2000s, culminating in "Killing in War" (2009), McMahan turned to the ethics of war. He challenged the traditional doctrine of the moral equality of combatants and developed an individualist, responsibility-sensitive account of liability to defensive harm. This phase placed him at the center of debates about humanitarian intervention, terrorism, and the moral obligations of soldiers.
Expansion into Animal Ethics and Longtermism
From roughly 2010 onward, McMahan increasingly engaged with animal ethics, the status of wild animals, and the moral weight of future generations. Interacting with effective altruism and longtermist thinkers, he extended his earlier framework about killing and harm to large-scale, temporally extended contexts, while questioning speciesism and exploring the implications of reducing suffering across species and time.
Institutional Leadership and Public Engagement
As White’s Professor of Moral Philosophy at Oxford and a prominent public intellectual, McMahan has supervised many leading younger philosophers, contributed to policy-related discussions on war and bioethics, and participated in interdisciplinary initiatives relating to law, animal welfare, and global priorities. This phase underscores his role not only as a theorist but also as an institutional shaper of contemporary moral and political philosophy.
1. Introduction
Jeffrey Paul McMahan (b. 1954) is a contemporary analytic moral philosopher whose work has reshaped debates about killing, war, and the moral status of animals. Writing largely within Anglophone moral and political philosophy, he is often grouped with Derek Parfit and other late 20th‑century theorists who combine metaphysical analysis with applied ethics, but he is distinctive in using these tools to challenge widely accepted legal and moral doctrines.
McMahan is best known for three clusters of ideas. First, he offers a systematic account of the ethics of killing that links the badness of death to questions about personal identity and psychological continuity over time. Second, he is a leading figure in revisionist just war theory, arguing that liability to being killed in war depends on an individual’s responsibility for an unjust threat rather than on combatant status alone. Third, he has become an influential voice in animal ethics and intergenerational morality, criticizing speciesism and exploring the implications of taking the suffering of nonhuman animals and future beings seriously.
His writings are widely cited in philosophy, bioethics, and law, and they have informed discussions of topics such as abortion, euthanasia, brain death, humanitarian intervention, and animal agriculture. Proponents regard his work as a model of rigorous yet practically engaged moral theory, while critics contend that his conclusions about self‑defense, war, and our duties to animals and future generations are overly demanding or conflict with deeply rooted moral intuitions and legal practices. The following sections examine his life, intellectual development, major works, central doctrines, and wider impact.
2. Life and Historical Context
McMahan was born on 30 August 1954 in Washington, D.C., into a period marked by the Cold War, decolonization, and the U.S. civil rights movement. These broader political developments formed the backdrop to later concerns in his work with war, nationalism, and global justice, though biographical scholarship has not established any simple causal link.
Education and Academic Positions
He studied in the United States before undertaking a DPhil in Philosophy at the University of Oxford, supervised by Derek Parfit and completed in 1986. This placed him at the center of a philosophical milieu in which questions about personal identity, rationality, and ethics were being pursued with new formal and argumentative rigor. McMahan subsequently held positions at institutions including Rutgers University and, from 2014, the prestigious White’s Professorship of Moral Philosophy at Oxford.
Historical-Philosophical Setting
His career unfolded during the consolidation of applied ethics as a major subfield, with growing interest in bioethics, environmental ethics, and the ethics of war. The end of the Cold War, humanitarian interventions in the Balkans and elsewhere, and debates about terrorism and counter‑terrorism created fertile ground for re‑examining just war theory. Simultaneously, the rise of animal ethics—influenced by Peter Singer, Tom Regan, and others—and later the emergence of effective altruism and longtermism provided contexts for McMahan’s engagement with animal suffering and future generations.
In this environment, his work interacted with, and sometimes opposed, dominant moral theories such as classical utilitarianism, contractualism, and rights‑based views. Supporters see his contributions as part of a broader late‑20th‑century shift toward highly revisionary moral theorizing, while critics situate him within a trend they regard as increasingly detached from ordinary moral practice.
3. Intellectual Development
McMahan’s intellectual trajectory is often described in distinct but overlapping phases, each building on earlier concerns while extending them into new domains.
From Personal Identity to the Ethics of Killing
Under Derek Parfit’s supervision at Oxford, McMahan developed a sustained interest in personal identity over time. Early work focused on how psychological continuity and connectedness bear on survival and prudential concern. This led him to questions about the badness of death and when killing is morally wrong, especially in cases involving fetuses, infants, the severely cognitively disabled, and those near brain death. During the 1980s and 1990s, articles that later fed into The Ethics of Killing refined his time‑relative interest account, connecting metaphysical debates to bioethical controversies.
Turn to War and Self-Defense
In the 1990s McMahan’s attention shifted toward self‑defense and the ethics of war. Puzzles about “innocent threats” and liability to defensive harm provided a bridge from interpersonal morality to armed conflict. Influenced by, but increasingly critical of, traditional just war theory, he developed an individually focused, responsibility‑sensitive framework that would culminate in Killing in War.
Expansion to Animals and the Future
From roughly 2010 onward, McMahan extended his ideas about killing, harm, and moral status to nonhuman animals and future generations. Engagement with animal ethicists and, later, with effective altruist and longtermist thinkers encouraged him to consider large‑scale suffering and temporally extended harms. His later essays retain the analytical style of earlier work but increasingly address systemic practices (e.g., factory farming, wild animal predation) and long‑run global risks.
Throughout these phases, commentators note a continuity: McMahan repeatedly uses fine‑grained distinctions about responsibility, psychological continuity, and interests to question conventional moral and legal categories.
4. Major Works
McMahan’s major works are often grouped into three thematic areas: killing and personal identity, the ethics of war, and nationalism and political community, with later essays extending his influence into animal ethics and future‑oriented issues.
Principal Books and Their Foci
| Work | Focus | Notes |
|---|---|---|
| The Ethics of Killing: Problems at the Margins of Life (2002) | Ethics of killing, personal identity, abortion, euthanasia, brain death | Systematic exposition of the time‑relative interest account and its implications for bioethics. |
| Killing in War (2009) | Just war theory, moral equality of combatants, liability in war | Canonical statement of revisionist just war theory, challenging orthodox principles. |
| The Morality of Nationalism (1997, co‑edited) | Nationalism, self‑determination, global justice | Collection that situates debates on national partiality and secession; McMahan contributes influential essays. |
Influential Articles
Several articles are widely treated as major works in their own right:
| Article | Theme | Significance |
|---|---|---|
| “Self‑Defense and the Problem of the Innocent Attacker” (1994) | Liability to defensive harm | Develops distinctions among culpable threats, innocent threats, and bystanders. |
| “The Ethics of Killing in War” (2004) | Bridge between killing and war ethics | Prefigures arguments later expanded in Killing in War. |
| “Our Fellow Creatures” (2005) | Anti‑speciesism, animal moral status | Articulates his opposition to speciesism and explores implications for human‑animal relations. |
| “The Meat Eaters” (2010) | Wild animal suffering | Popular but philosophically significant discussion of moral responses to natural predation. |
Scholars sometimes contrast The Ethics of Killing and Killing in War: the former integrates metaphysics with bioethics, while the latter applies his liability framework to collective violence. Critics have questioned both the practical implications and alleged revisionism of these works; supporters regard them as central reference points in contemporary moral and political philosophy.
5. Core Ideas on Killing and Personal Identity
McMahan’s work on killing is anchored in a specific view of what we are and how we persist over time, and he uses this to explain both the badness of death and the permissibility of killing.
Personal Identity and the Time-Relative Interest Account
Influenced by Parfit, McMahan treats psychological continuity and connectedness—relations of memory, intention, character, and other mental features—as central to survival and prudential concern. He argues that what matters morally is not simply numerical identity but the strength of psychological unity between present and future stages of a being.
His time‑relative interest account holds that the badness of a person’s death depends on the extent to which they now stand in these prudential unity relations to their future life:
“Our concern about the badness of death for an individual should vary with the extent to which that individual’s present psychological life is related to his future life…”
— Jeff McMahan, The Ethics of Killing, p. 165
On this view, death is generally worse when it cuts off a rich, psychologically continuous future; it is typically less bad for beings whose present ties to their future are weak (for example, early fetuses or individuals with severely diminished consciousness), though McMahan notes that other moral considerations may still weigh against killing.
Margins of Life and Moral Status
Applying this framework, McMahan explores “margins of life” cases: abortion, neonatal euthanasia, severe cognitive disability, and brain death. He distinguishes between being a person (possessing certain psychological capacities) and merely being a biological human organism, arguing that personhood and psychological capacities are central to many moral judgments about killing.
Critics object that this approach risks devaluing some humans or underestimates the moral significance of merely biological human life. Alternative views emphasize inherent human dignity, species membership, or potential personhood. Supporters contend that McMahan’s account better tracks our intuitions about varying harms of death and clarifies contested bioethical issues.
6. Revisionist Just War Theory and Self-Defense
McMahan is a leading proponent of revisionist just war theory, which reexamines traditional principles about killing in war by grounding them in individual liability and self‑defense.
Liability to Defensive Harm
In “Self‑Defense and the Problem of the Innocent Attacker,” McMahan argues that liability to defensive harm depends on moral responsibility for an unjust threat, not merely on causally posing danger:
“Liability to defensive harm is not a matter of causal responsibility alone but of moral responsibility…”
— Jeff McMahan, “Self‑Defense and the Problem of the Innocent Attacker,” Ethics 104 (1994), p. 252
He distinguishes:
| Category | Description | Moral Implication (on his view) |
|---|---|---|
| Culpable Threat | Knowingly or negligently imposes unjust threat | Typically liable to defensive harm, sometimes even to lethal force. |
| Innocent Threat | Causes threat without moral responsibility (e.g., manipulated attacker, falling body) | Liability greatly reduced or absent; permissibility of harming is contested and highly constrained. |
| Bystander | Neither causes nor is responsible for threat | Generally not liable; harming usually impermissible. |
This fine‑grained structure underpins his broader approach to war.
Critique of the Moral Equality of Combatants
Traditional just war theory holds that lawful combatants on all sides are moral equals: each may kill enemy combatants, provided jus in bello rules are followed. McMahan challenges this, arguing that soldiers fighting for an unjust cause typically lack a right to kill, because they are responsible for contributing to an unjust threat. In Killing in War he extends the self‑defense framework:
- Just combatants: fighting to avert or rectify unjust aggression may be liable to some constraints but can often permissibly target unjust combatants.
- Unjust combatants: usually not morally permitted to kill even enemy soldiers, because their actions help prosecute an unjust war.
Revisionist theorists sympathetic to McMahan see this as aligning war ethics with ordinary self‑defense. Critics contend that it is too demanding on soldiers, ignores epistemic limitations about just cause, or threatens the feasibility of international humanitarian law, which relies on treating combatants symmetrically.
7. Animal Ethics and Future Generations
McMahan’s later work extends his concerns about killing and harm to nonhuman animals and future beings, engaging with debates in animal ethics, effective altruism, and longtermism.
Anti-Speciesism and Animal Moral Status
McMahan rejects speciesism, the view that species membership alone justifies giving greater moral weight to human interests:
“Speciesism is, in itself, no more defensible than racism or sexism; what matters morally are the interests and capacities of individuals…”
— Jeff McMahan, “Our Fellow Creatures,” The Journal of Ethics 9 (2005), p. 363
He argues that what matters are individuals’ capacities for experiences (such as pleasure, pain, and certain forms of consciousness) and their time‑relative interests, not their biological category. This position supports strong obligations to reduce animal suffering, including in factory farming and other human practices.
Critics worry that anti‑speciesism undermines special obligations to humans or is incompatible with common moral intuitions about life‑saving priorities. Others question how to weigh different animals’ interests given varying cognitive capacities.
Wild Animals and Natural Suffering
In “The Meat Eaters” and related work, McMahan raises the controversial possibility that humans might sometimes have reason to intervene in nature to reduce wild animal suffering, for example by influencing predator‑prey dynamics. Proponents see this as a consistent extension of concern for suffering; opponents argue that large‑scale intervention risks ecological harm, violates respect for wild nature, or exceeds human epistemic limits.
Future Generations and Longtermism
McMahan also addresses obligations to future generations, including the ethics of creating new beings and large‑scale future harms. While not a canonical longtermist, he interacts with longtermist arguments about prioritizing the far future, exploring how the time‑relative interest account and concerns about suffering apply across long temporal horizons. Some commentators align his work with suffering‑focused longtermism; others stress his caution about speculative scenarios and the moral relevance of existing individuals’ interests.
8. Methodology and Argumentative Style
McMahan’s methodology combines the tools of analytic philosophy with a willingness to reach revisionary conclusions about everyday moral and legal beliefs.
Case-Based, Fine-Grained Analysis
He frequently employs hypothetical cases—for example, innocent attackers, falling bodies, or stylized battlefield scenarios—to isolate morally relevant factors such as responsibility, intention, and causal contribution. These cases are often incrementally varied to test the robustness of intuitions and to reveal implicit principles.
This method leads to fine‑grained distinctions: between types of threats, degrees of responsibility, and varying strengths of time‑relative interests. Supporters regard this as clarifying; critics argue that it risks over‑subtlety or dependence on controversial intuition judgments.
Integration of Metaphysics and Normative Ethics
A hallmark of his style is the integration of metaphysical claims about persons and identity with normative questions about permissibility and harm. Rather than treating personal identity as an abstract puzzle, he uses it to inform views on abortion, euthanasia, and war. Some philosophers praise this synthesis as exemplary of “serious” applied ethics; others contend that controversial metaphysical premises render his ethical conclusions unstable or overly speculative.
Revisionary but Policy-Aware
McMahan often accepts that his conclusions conflict with common sense and established legal doctrines, especially about combatant equality and the permissibility of killing in war. Yet he also engages with practical constraints, including epistemic uncertainty and institutional feasibility. In discussions of war and animal ethics, he distinguishes between ideal moral theory and what individuals or institutions should do given current conditions.
His prose is typically clear, argumentative, and densely reasoned, with extensive engagement with opponents. This style has made his work central in seminar‑room debates and influential in interdisciplinary discussions involving law, political theory, and bioethics.
9. Impact on Moral and Political Philosophy
McMahan’s work has had substantial influence on several subfields of moral and political philosophy, as well as on adjacent disciplines such as law and bioethics.
Reshaping Debates on Killing and Bioethics
In bioethics, The Ethics of Killing is widely cited for its systematic integration of personal identity and normative theory. It has informed discussions of abortion, neonatal euthanasia, organ donation, and end‑of‑life decisions. Supporters credit him with clarifying how different accounts of personal identity yield divergent ethical verdicts. Critics, including defenders of sanctity‑of‑life and inherent dignity doctrines, see his framework as overly permissive toward some forms of killing or insufficiently respectful of human life irrespective of psychological capacities.
Establishing Revisionist Just War Theory
McMahan’s influence is especially pronounced in the emergence of revisionist just war theory. Many contemporary philosophers of war—such as Cécile Fabre, Helen Frowe, and others—develop, defend, or critique positions framed explicitly in response to his liability‑based approach. Legal scholars and military ethicists have also engaged his challenge to the moral equality of combatants, particularly in relation to targeted killing, humanitarian intervention, and soldiers’ responsibilities.
Contributions to Animal Ethics and Longtermism
His anti‑speciesist arguments and discussions of wild animal suffering have contributed to a growing literature on animal ethics and wild animal welfare, influencing both academic debate and some advocacy organizations. In longtermist and effective altruism circles, his analyses of future‑oriented duties and large‑scale suffering inform discussions about prioritizing interventions and evaluating existential and suffering risks.
Institutional and Pedagogical Influence
As a senior figure at Rutgers and later White’s Professor at Oxford, McMahan has supervised and collaborated with many philosophers who now shape debates on killing, war, and animals. His seminars and collaborative projects (including initiatives related to animals, law, and ethics) have fostered cross‑disciplinary engagement. Some observers view his career as emblematic of a broader shift toward highly analytical yet practically engaged moral theory; others worry that such work still remains too removed from non‑Western perspectives and global South contexts.
10. Legacy and Historical Significance
Assessments of McMahan’s legacy emphasize both his direct theoretical contributions and his role in broader shifts within contemporary moral philosophy.
Reframing the Ethics of Killing and War
Historians of philosophy often identify McMahan as a central figure in reframing the ethics of killing around time‑relative interests and psychological continuity, and in transforming just war theory into a more individualized, liability‑focused enterprise. Some commentators suggest that future textbooks will routinely contrast “traditional” and “revisionist” just war theory, with McMahan as a canonical representative of the latter.
Influence on the Moral Status of Nonhumans and the Future
His challenges to speciesism and his willingness to take wild animal suffering and future beings seriously are seen by many as indicative of a long‑term shift toward a more inclusive and temporally extended moral community. Whether or not his specific views prevail, scholars anticipate that questions he helped foreground—about intervening in nature, about large‑scale suffering, and about population‑level ethics—will remain central to 21st‑century moral theory.
Ongoing Debates and Critiques
McMahan’s proposals have also provoked sustained critical engagement. Traditional just war theorists, deontologists emphasizing human dignity, and theorists concerned with feasibility and institutional stability challenge his more revisionary implications. Some legal scholars argue that his norms are too demanding for international law; others see his work as a valuable guide for incremental reform.
Overall, his historical significance is typically characterized in terms of methodological exemplarity and agenda‑setting. He exemplifies a style of moral philosophy that combines rigorous argument, metaphysical sophistication, and applied concern, and he has helped set the agenda for debates on killing, war, animals, and the far future that are likely to continue well beyond his own career.
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@online{philopedia_jeff_mcmahan,
title = {Jeffrey Paul McMahan},
author = {Philopedia},
year = {2025},
url = {https://philopedia.com/thinkers/jeff-mcmahan/},
urldate = {December 11, 2025}
}Note: This entry was last updated on 2025-12-10. For the most current version, always check the online entry.