Martha Nussbaum is a very, very big deal, the kind of philosopher who, when she publishes a book, makes waves well beyond the ivory towers of academia. Her new volume, Justice for Animals, plunges into the animal welfare debate, billing itself as a “revolutionary new theory” in how we humans think about other animals. Which makes it all the more surprising that, at its heart, her theory isn’t very revolutionary at all.
Nussbaum, whom the New Yorker once described as “monumentally confident,” contends that pretty much everyone has been thinking about animals wrong — including animal lovers. She rejects the leading ethical approaches to animals and urges us to accept hers: the capabilities approach. And as a philosopher who is also steeped in the law, she wants her theory to change real-world policy.
Nussbaum first co-developed the capabilities approach in the 1980s with humans in mind, working with its original architect, the Nobel-winning economist Amartya Sen. The theory argues that a just society should give each human the chance to flourish, which requires the opportunity to access some core entitlements to at least some minimum degree — things like good health and physical safety that any living thing requires, but also social relationships and play. These aren’t random; they’re things that human beings have specific reason to value because of the type of creatures we are.
Now, she wants us to extend this approach to other species. Each species will have its own list of core entitlements, tailored to its unique form of life. The animal’s nature — its intrinsic capacities — would decide how it has the right to be treated, as opposed to us humans deciding how we think it should be treated.
The appeal of the capabilities approach is that it gives us clear rules about what we can and can’t do to animals, an ethical formula that can claim to be rooted in something intrinsic or objective. Which would be nice: Life is so complicated and messy; it’s comforting to have a formula!
But ultimately, it does humanity a disservice. The obligations we feel to animals can’t be captured by any immutable formula because they don’t only flow from the animals’ intrinsic capacities; they’re also shaped by the relationships those animals can have with us, and by our own historical, economic, and cultural conditions, which are always changing.
By clinging to the dominant style of argument in animal ethics — a style that says our obligations to animals are forced on us by the nature of animals themselves or even the nature of reasonableness itself — Nussbaum’s theory ends up leading to some iffy conclusions. It leads to a focus on helping individual animals, not species. And it prompts us to consider the idea that we should intervene to help not just those animals we’ve domesticated, which are utterly dependent on human beings, or those directly harmed by our actions, like endangered species, but also those trillions of animals that suffer and have always suffered in the wild.
By the end of the book, Nussbaum is declaring things like this: “To say that it is the destiny of antelopes to be torn apart by predators is like saying that it is the destiny of women to be raped. Both are terribly wrong.”
Like I said, iffy.
Let’s back up a bit: What are the existing ethical approaches to animals that Nussbaum rejects, and where does she think they fail?
One is what she calls the “So Like Us” approach. It says we should particularly protect animals that display intelligence and reason like us. One group that embraces this approach is the Nonhuman Rights Project, which tries to win legal personhood rights for species like elephants and chimpanzees with arguments that are primarily based on the intelligence of those species.
But using human-like intelligence as the yardstick for moral value is an old mistake: Ever since Aristotle developed the idea of the Scala Naturae, a “natural ladder” that classified some animals as higher life forms and others as lower, humans (at least in the West) have repeatedly underestimated the cognitive complexity of other species. Suffering from an anthropocentric bias, we tend to think something counts as intelligence only when it looks like human intelligence. But researchers are increasingly recognizing that every species has its own brand of smarts. Each is perfectly adapted to its unique environment and needs.
The second approach Nussbaum rejects is that of the 18th-century British utilitarian philosopher Jeremy Bentham. The right question to ask about animals, Bentham argued, is not “Can they reason?” but “Can they suffer?” So instead of using intelligence as the yardstick for moral value, the utilitarian camp uses sentience: the ability to experience pain or pleasure. It says we should minimize pain for any creature that can feel it, a position most prominently held today by the Australian ethicist Peter Singer.
Nussbaum likes the emphasis on sentience. She thinks it makes sense to view it as a clear dividing line in nature: Only creatures with sentience deserve rights. But she rejects the utilitarians’ decision to calculate pain and pleasure as an aggregate, with the aim of producing the greatest good for the greatest number. As utilitarian thought experiments show, this approach can produce a result that’s great on net even while making some individuals deeply miserable. That neglects the importance of individual lives, treating them as interchangeable cogs.
Nussbaum is determined to preserve the inviolability of each individual animal, and this leads her to investigate a third major theory: that of Immanuel Kant, as read through the contemporary philosopher Christine Korsgaard. According to Kant, you should never treat a human being as a means to an end; people are ends in themselves. It would never be right to harm one person even if it benefits many on net. Korsgaard takes that basic idea and extends it to animals.
It’s a move Nussbaum applauds. But she takes issue with the fact that Korsgaard still gives special status to humans because of our ability for complex ethical reasoning. Korsgaard says animals aren’t capable of that, so they can only be passive citizens of the world.
“I think that is just much too simple because animals are very active in indicating what they need and want,” Nussbaum told me in an interview late last year. “They have marvelous, complicated ways of speaking or signaling … and we should be listening to that and taking account of that.”
So Nussbaum salvages from the utilitarians an emphasis on sentience, and from Kant an emphasis on the inviolable rights of each end-in-itself creature. She thinks combining these two ingredients sets her up for a better approach: her capabilities approach.
But she ends up hamstrung by the limitations of each view. Sentience isn’t the bright dividing line utilitarians believe it is, and Kantians fail to reckon with the need to balance competing needs with each other.
Sentience has always been a squishy category. Some experts define it as basic sensitivity — your ability to sense things, like the color red. Others say it’s your ability to feel pleasure or pain. Nussbaum defines it more broadly: You’re sentient if you have a subjective point of view on the world, and there’s something that it’s like to be you (whereas the answer to “what is it like to be a rock?” is “nothing”).
It makes sense that she’d embrace sentience as a dividing line in nature. She says justice requires giving each creature the chance to fulfill its significant strivings, so she needs a way to tell which creatures are capable of significant striving.
But if we think of sentience in such binary terms — either you’ve got it or you don’t — then we create a sharp border, where those who are “in” have a right to be treated justly, and those who are “out” don’t. This should give us pause because every time we humans have come up with a way of dividing up nature, later generations have overturned it.
Historically, societies started by thinking that being a male human is what matters, and then expanded the notion to believe that being a human is what matters, and then that being an intelligent animal is what matters, and now that being sentient is what matters. “In light of that history, we should be a little skeptical of our current impression that we happen to now be fully morally enlightened and are including everybody we should be including,” Jeff Sebo, a professor of environmental studies and philosophy at New York University, told me in 2021.
Philosophers and researchers increasingly believe a binary idea of sentience doesn’t fit well with what we see when we look closely at living things in the natural world. That’s because the more we learn about different species, even simple ones, the more we find glimmers of sentience.
For example, people have long thought of fish as emotionally vacant, but recent experimental studies challenge that view; it turns out romantic breakups really suck, even for fish. The same goes for octopuses, lobsters, and crabs, all of which the British government now recognizes as sentient. The 10 quintillion insects on the planet may be sentient, too, evidence suggests. In recent years, some scientists have even argued that plants have sentience.
Some thinkers have adapted by proposing that sentience comes in degrees. The primatologist Frans de Waal has suggested there are three levels of sentience: sensitivity, experience, and consciousness. And the philosopher Daniel Dennett has hypothesized that “‘sentience comes in every imaginable grade and intensity, from the simplest and most ‘robotic,’ to the most exquisitely sensitive, ‘hyper-reactive’ human.”
But even this is probably too simplistic. If we say sentience comes in degrees, we’re saying it lines up neatly on a single scale, running from “more sentient” to “less sentient,” and suddenly we’re back on Aristotle’s Scala Naturae. There is reason to doubt whether a creature’s sentience can be measured in terms of just one metric, like its number of neurons. Rather than viewing sentience as running on a single scale, some philosophers now argue that sentience is “a multi-dimensional phenomenon.”
If they’re right, sentience will go the way of intelligence. Just as people like Nussbaum want to ditch the older framing of “this species is smarter than that species” in favor of “different species are smart in different ways (that are best suited to their form of life),” we’ll want to ditch the framing of “this species is more sentient than that species” for “different species exhibit different forms of sentience (that are best suited to their form of life).”
But Nussbaum doesn’t go this route. She is too committed to viewing each individual creature as a Kantian “end in itself” — and that doesn’t come in degrees. It only has one dimension. You either are an “end in yourself” or you’re not.
Nussbaum writes that her view sees “animal lives as having intrinsic value” — with the caveat, “ethically, though not in my political theory.” She claims this is just her personal belief and it doesn’t factor into her theory.
“What I think metaphysically has nothing to do with it,” she told me. “Because my overall position, in my view, is that in political principles and legal principles, we should never include any controversial metaphysical positions. This is what John Rawls said famously in Political Liberalism — that if we’re in a pluralistic society where people differ about metaphysics, we should never include in our political principles these controversial metaphysical claims about which people differ.”
But her controversial claims do factor into her theory. In fact, her whole theory has a strong flavor of moral realism, a doctrine that says there is such a thing as objective moral values. Her underlying premise is that we can find out what objective moral rights an animal has by examining that animal’s objective capacities. The animal’s nature forces obligations on us.
In her book, Nussbaum critiques philosophers who take a more anti-realist stance, who argue that value is a subjective human creation, that it doesn’t exist “out there” to be discovered. According to Nussbaum, that’s a controversial position and should be left out.
But if anti-realism is a controversial position, Nussbaum’s realism is equally controversial. And it leads her down some very controversial paths.
For one thing, Nussbaum argues that “for ethics, it is the individual creature that is the end, not the species.” She does acknowledge that preserving an endangered species may have instrumental value, like scientific or aesthetic value. But she insists that a species doesn’t “count as an end for the purposes of political justice” because “a species has no point of view on the world.”
It’s true that a species doesn’t feel or suffer; that’s what the individual animals that make up a species do. But the argument that only individual animals can be wronged runs aground when the needs of different species conflict.
This is a problem Australia has recently had to face. Hundreds of millions of feral rabbits — which trace back to just 24 rabbits brought over by an English settler in 1859 — have driven some of the country’s native plant species to the brink of extinction and altered entire ecosystems by munching away at vegetation. In 2011, the Australian government noted that rabbits had “reduced Philip Island to bedrock, leaving at least two plants locally extinct,” and announced that it would kill rabbits to conserve ecosystems.
If Australia had applied Nussbaum’s view, it might have been warier about killing the rabbits, even if it meant some native species were decimated. Rabbits are sentient individuals with a point of view on the world, but ecosystems or plants don’t have a point of view on the world, according to Nussbaum, so they are deemphasized in her theory. Placing so much emphasis on who is a sentient end in itself could tip the scales in favor of individual creatures even when an entire species is at stake.
Viewing each animal as an end in itself also inflects Nussbaum’s view on our responsibility toward animals in the wild. Partly, she’s driven by the very reasonable observation that there are hardly any truly “wild” spaces left on Earth: Humans control habitats on land, in the sea, and in the air, and through climate change we damage those habitats. It’s disingenuous to say we have no duty to consider the well-being of wildlife. “Wild” versus “domesticated” is a misleading split.
But it gets weird when Nussbaum urges us to think not only about remediating human harms, but also about proactively protecting wild animals. Natural types of animal suffering like starvation and disease, which were a fact of life on Earth since well before the first Homo sapiens, trouble her. For her, even the pain of an individual antelope as it’s eaten by a predator is a horrible problem. (Remember her quote from earlier? “To say that it is the destiny of antelopes to be torn apart by predators is like saying that it is the destiny of women to be raped.”) She’s not just worried about whether antelopes as a species survive. She’s worried about each and every end-in-itself antelope, trying to survive in a natural world that is red in tooth and claw.
So she says “we must use our knowledge — wisely and deliberately — to protect wild animal lives.” When it comes to predation, she acknowledges there are good reasons to hold off on intervening for now (for all we know, getting rid of the antelopes’ predators might topple the whole ecosystem, harming the very animals we meant to protect). But there are other interventions she’s more bullish about, like using contraceptives for wild animals to tackle population imbalances.
She gave me the example of a habitat where elks have reproduced rapidly. Now the elks don’t get enough to eat, and they’re going hungry. “Suppose we concluded that humans have not really caused this problem. I still think that animal contraception should be investigated as part of the solution,” she told me.
Overall, when it comes to intervening in the wild, she writes, “How much further can we go in this direction? We need to press this question all the time.”
Other philosophers push back on that stance. Take Elizabeth Anderson, who was once Nussbaum’s student at Harvard and who now teaches at the University of Michigan. She subscribes to the school of thought in philosophy known as pragmatism, which sees moral truths as contingent, not objective. This results in a story about animals that is very different from the one Nussbaum tells.
Anderson points out that for most of human history, we couldn’t have survived and thrived without killing or exploiting animals for food, transportation, and energy. The social conditions for granting animals moral rights didn’t really exist on a mass scale until recently (although certain non-Western societies did ascribe moral worth to some animals).
“The possibility of moralizing our relations to animals,” she writes, “has come to us only lately, and even then not to us all, and not with respect to all animal species.”
Anderson notes that we feel different levels of moral obligation to different species, and that has to do not only with their intrinsic capacities like intelligence or sentience, but also with their relationships to us. It matters whether we’ve made them dependent on us by domesticating them — like the more than 30 billion domesticated chickens alive at any given time, most of them suffering terrible pain at our hands — or whether they live in the wild. It also matters whether they’re fundamentally hostile to us.
For example, if you find bedbugs in your house, nobody expects you to say, “Well, they’re maybe sentient and definitely alive, so they have moral value. I’ll just live and let live!” It is absolutely expected that you will exterminate them.
Why? Because with vermin, Anderson writes, “there is no possibility of communication, much less compromise. We are in a permanent state of war with them, without possibility of negotiating for peace. To one-sidedly accommodate their interests … would amount to surrender.”
Anderson’s point is not that animals’ intelligence and sentience don’t matter. It’s that lots of other things matter, too, including our own ability to thrive.
So her view doesn’t require us to draw one bright line through nature. Anderson is inclined to value all living things, including plants, which she notes clearly have interests. And she’s inclined to think protecting a species in some cases can justify getting rid of non-endangered individuals, as in the case of Australia’s action against invasive rabbits. Individuals’ sentience isn’t a trump card.
“There’s a plurality of values at stake here, and I’m disinclined to think that any single one of them necessarily overrides all the others,” Anderson told me. “It depends on the context.”
Anderson’s insistence on taking seriously a plurality of values also guides her approach to the question of animals in the wild. She thinks it’s bizarre to worry about wild animals suffering at the hands of predators. Suffering, after all, “is inherent to the animal condition,” she told me. “The idea of minimizing suffering becomes a single-minded goal that doesn’t really grasp the vital importance of predators for ecosystems.”
It’s possible to wed Anderson’s inclination to value all living things and the ecosystems that support them with Nussbaum’s capabilities approach. You can say, “This is the human form of life, and to some extent it is different from other forms of life. All lives are uniquely wonderful in their own way” — and then to apply the capabilities approach by respecting each and every organism’s form of life as much as you can.
But there are two very understandable fears about adopting this view.
One is that it’s just going to make things, well, really hard! If every living thing is potentially invested with moral value, that seems to impose on us a crushing amount of responsibility. How could we even move at all in such a world, knowing that every step we take could change that world and the animals that live in it? What would we do when the needs of different species conflict?
To which Anderson essentially responds, that’s life. The best we can do is look at creatures’ intelligence and sentience and aliveness and relationships to us as clues about their importance. But it doesn’t tell us how to weight those clues and what to do when they conflict.
“There’s no simple formula,” Anderson told me. “I think that’s a hopeless quest.”
The other fear you might have is the inverse: Instead of worrying that people will now care about everything, you might worry that people will now care about nothing. If you say creatures do not have objective rights, why shouldn’t we treat nature as a free-for-all — which is largely what humans have done through most of our existence?
But that’s the point: History shows that saying creatures have objective rights doesn’t magically convince people to treat animals well. Most people are not moral philosophers and are not swayed by a priori reasoning alone. Where they change their behavior to be more considerate of other beings, it’s often because the economic and cultural constraints operating on them have changed.
For example, in the early 1900s there was still a perceived need for women to stay home and perform household labor. But by the middle of the century, the invention of new household appliances — like the washing machine or dishwasher — catalyzed the emancipation of women by undercutting the perceived need for them to labor so long at home.
Similarly, if a society feels it needs to eat animal products to get enough nutrition, it might have a hard time viewing all animals as morally valuable. But if a society doesn’t feel it needs to eat animal products, it may have an easier time looking upon animals and feeling awe or empathy. Our ability to access those sorts of emotions is constrained or bolstered by the context we live in.
According to that line of thinking, even the cleverest moral arguments may have less influence on animal welfare than the advent of cheap and delicious plant-based meat, like Beyond Meat and Impossible Burgers, as well as plant-based dairy and eggs. This type of tech innovation could free us up to see animals as creatures inspiring awe or empathy, making it easier to adopt kinder practices toward them.
Ultimately, concern for animals is not forced on us by the nature of animals themselves. And if it’s not forced on us, that means it has to be a choice. Perhaps the best we can do is influence economic and cultural conditions to make it more possible for people to choose to care.
This is an uncomfortable place for most philosophers to land. Many see it as their job to come up with grand theories, totalizing systems that can compel a certain kind of ethical behavior. Nussbaum writes that her capabilities approach “aims to supply a virtual constitution to which nations, states and regions may look in trying to improve (or newly frame) their animal-protective laws.”
But even the most convincing of grand theories have never managed on their own to compel everyone to behave a certain way. And any grand theory will be unconvincing for those of us who ask: If morality is conditioned by our cultural context, why would there ever be one universal, timeless formula that tells us how to slice up nature into clear moral categories?
Nussbaum’s capabilities approach doesn’t need to present itself as a grand theory in order to make a helpful contribution to our world. Although it won’t, on its own, motivate concern for animals, it can be a very useful framework when we’re trying to figure out how to express our concern. Beyond that, philosophy actually has a crucial role to play: If it acknowledges that our moral beliefs are conditioned by cultural context, it can help show us that there was nothing inherently “normal” or “natural” about our ancestors’ cruel practices toward animals, and that those practices are mostly not necessary now. It can free up our culture to tell a new story about ourselves and other animals.
Sigal Samuel is a senior reporter for Vox’s Future Perfect and co-host of the Future Perfect podcast. She writes primarily about the future of consciousness, tracking advances in artificial intelligence and neuroscience and their staggering ethical implications. Before joining Vox, Sigal was the religion editor at the Atlantic.