This conflict between the view of the other animals as a usable resource and the view of them as fellow creatures has reached new extremes in the contemporary world. On the one hand, we treat at least some animals—companion animals—as members of the family to an extent that is probably unprecedented in human history. Companion animals live in our homes, with special furniture and toys dedicated to their use. Michael Pollan, in The Omnivore’s Dilemma, reports that half of the dogs in America receive Christmas presents these days.² Many companion animals nowadays have health insurance and are given expensive medical treatments for serious illnesses. And when they die, they are often buried in cemeteries by their mourning human companions.

And yet these same animals are abandoned by the millions, ending up in shelters where they will probably be euthanized, or in laboratories where they face even worse fates, simply because it has become inconvenient for their owners to keep them. And modern factory farming represents the most widespread and extensive form of cruelty to animals that our species has practiced yet. Many factory farm animals live in densely overcrowded conditions, indoors, with their excrement and their dead left among them. Farmers cut off the beaks of chickens and the tails of pigs, without anesthetics, as ways to control the aggression produced by this overcrowding.³ Others, such as some pigs and calves, although they are highly social, live alone in crates too small for them to turn around in. Many chickens spend most of their lives in pain, because they are fattened much too quickly, and their legs cannot comfortably bear their weight. Chickens deemed useless are sometimes ground up alive. These industrial food-processing techniques make it possible to produce meat cheaply, and as a result, despite the cruelty of the methods, people have begun to eat meat in unprecedented quantities.

Those who wish to urge the cause of better treatment for the other animals usually urge the continuity, the similarity, between human beings and the other animals. They deny that there is anything special about human beings that justifies us in using the other animals as means to our own ends. Those who wish to fend off these attacks have sometimes insisted on sharp human/animal differences. My own view falls between these two positions. I believe that there is an important difference between human beings and the other animals. But instead of being a difference that justifies our treatment of the other animals as resources, it is a difference that we can live up to only by treating them as fellow creatures.

In the Dialogues Concerning Natural Religion, his classical discussion of the argument from design, David Hume presents us with three characters who represent different positions with regard to philosophical theology: Demea, who at first favors the traditional a priori proofs for God’s existence, and later turns to a fideistic position; Cleanthes, who champions the argument from design as an empirical proof of God’s existence; and Philo, the skeptic, who attacks all of the arguments and keeps the reader guessing about what his own views really are. So much is well known to everyone who reads the Dialogues, but few readers notice that these three characters also represent three different attitudes one might take about whether we should consider the welfare of the other animals when we ask whether there is a beneficent God.

Cleanthes gives his most resounding statement of the argument from design when he says:

Look around the world: Contemplate the whole and every part of it: You will find it to be nothing but one great machine, subdivided into an infinite number of lesser machines, which again admit of subdivisions to a degree beyond what human senses and faculties can trace and explain. All these various machines, and even their most minute parts, are adjusted to each other with an accuracy which ravishes into admiration all men who have ever contemplated them. The curious adapting of means to ends, throughout all nature, resembles exactly, though it much exceeds, the productions of human contrivance; of human design, thought, wisdom, and intelligence. Since therefore the effects resemble each other, we are led to infer, by all the rules of analogy, that the causes also resemble, and that the Author of Nature is somewhat similar to the mind of man. . . . (DNR 15)⁴

Later, in what is obviously intended as a parody of this passage, the skeptical Philo says:

Look round this universe. What an immense profusion of beings, animated and organized, sensible and active! You admire this prodigious variety and fecundity. But inspect a little more narrowly these living existences, the only beings worth regarding. How hostile and destructive to each other! How insufficient all of them for their own happiness! How contemptible or odious to the spectator! The whole presents nothing but the idea of a blind nature, impregnated by a great vivifying principle, and pouring forth from her lap, without discernment or parental care, her maimed and abortive children! (DNR 74)

Part of Philo’s point in this passage, a point he has been insisting upon explicitly throughout the Dialogues, is that the world resembles a gigantic organism at least as much as it resembles a gigantic invention or machine. But Philo is also making a point about nonhuman animals. Here, and whenever the question of our empirical evidence for or against a beneficent God arises, Philo includes, as an essential part of that evidence, reflections on the fate of the other animals.

It is actually Demea, the most orthodox of the three characters, who first introduces the question of divine beneficence, and its relation to the fate of the other animals, into the discussion. In the wake of Philo’s attack on the a priori arguments for God’s existence, Demea rather unguardedly proposes that the source of religious faith is the misery of human existence. Awareness of his own misery, he suggests, leads man to “seek protection from that Being on whom he and all nature are dependent” (DNR 59). And he adds:

And why should man . . . pretend to an exemption from the lot of all other animals? The whole earth . . . is cursed and polluted. A perpetual war is kindled amongst all living creatures. Necessity, hunger, want stimulate the strong and the courageous: fear, anxiety, terror agitate the weak and the infirm. The first entrance into life gives anguish to the new-born infant and to its wretched parent: weakness, impotence, distress attend each stage of that life, and it is, at last, finished in agony and horror. (DNR 59)

Philo pretends to agree with Demea about this, and adds:

Observe, too, the curious artifices of nature in order to embitter the life of every living being. The stronger prey upon the weaker and keep them in perpetual terror and anxiety. The weaker, too, in their turn, often prey upon the stronger, and vex and molest them without relaxation. Consider that innumerable race of insects, which are either bred on the body of each animal, or flying about infix their stings in him. These insects have others still less than themselves which torment them. And thus on each hand, before and behind, above and below, every animal is surrounded with enemies which incessantly seek his misery and destruction. (DNR 59–60)

Philo is mocking Demea’s efforts to ground religious faith on the horrors of nature, but he is also mocking Cleanthes’ version of the argument from design. Instead of machine embedded within machine, contrivance within contrivance, nature presents us with torment embedded within torment. Philo concludes:

. . . neither man nor any other animal is happy; therefore [God] does not will their happiness. His wisdom is infinite; He is never mistaken in choosing the means to any end; But the course of nature tends not to human or animal felicity: Therefore, it is not established for that purpose. (DNR 63)

How do Cleanthes and Demea respond to this argument? Cleanthes agrees with Philo’s point that empirical evidence for a beneficent God is required, but he either sets aside, or simply fails to notice, Philo’s insistence that the fate of the other animals should be included in that evidence. His response is: “If you can make out the present point, and prove mankind to be unhappy or corrupted, there is an end at once of all religion.” And, a few lines later, he adds: “The only method of supporting divine benevolence . . . is to deny absolutely the misery and wickedness of man” (DNR 64; both my emphases).

Why only “mankind” and “man”? Earlier in the Dialogues, Cleanthes voices the traditional religious view that the animals were created for human convenience (DNR 52). Does Cleanthes think that if the other animals were created for our use, then it doesn’t matter whether their lives are comfortable or not? He doesn’t say, and his failure to respond to the issue Philo raises makes it hard to determine what he thinks. Demea at least is clear. He thinks that both human beings and the other animals are miserable in this life, but that human beings are promised recompense in another life (DNR 64).⁵ His God is a god who is beneficent to humanity alone.

Philo speaks for Hume. Throughout his philosophy, Hume emphasizes the commonality between human beings and the other animals. Perhaps no other philosopher before the twentieth century took the idea that human beings are animals so seriously, or reminded us of it so often. In the Treatise, Hume ends his discussion of human understanding with a section devoted to the reason of animals (T 1.3.16), and he ends his discussions of pride and humility, love and hate, with a discussion of those passions as they appear in the other animals (T 2.1.12, 2.2.12). And in all these cases, he argues that there are no marked differences between human beings and the other animals. Human beings admire the instincts of animals, Hume says, while we are not astonished at our own power of reason. But, he says, “to consider the matter aright, reason is nothing but a wonderful and unintelligible instinct in our souls, which carries us along a certain train of ideas . . .” (T 1.3.16, p. 179).

Interestingly, Hume does not credit nonhuman animals with a moral sense. But he does think that animals have the same tendency to sympathy that, according to his own moral theory, becomes the moral sense in human beings once it is regulated by reason.⁶ The other animals lack only the capacity for taking up an impartial view that gives human sympathetic responses their moral character.

Were there a species of creatures intermingled with men, which, though rational, were possessed of such inferior strength, both of body and mind, that they were incapable of all resistance, and could never, upon the highest provocation, make us feel the effects of their resentment; the necessary consequence, I think, is that we should be bound by the laws of humanity to give gentle usage to these creatures, but should not, properly speaking, lie under any restraint of justice with regard to them. . . . Our intercourse with them could not be called society, which supposes a degree of equality; but absolute command on the one side, and servile obedience on the other. Whatever we covet, they must instantly resign: Our permission is the only tenure, by which they hold their possessions: Our compassion and kindness the only check, by which they curb our lawless will: And as no inconvenience ever results from the exercise of a power, so firmly established in nature, the restraints of justice and property, being totally useless, would never have place in so unequal a confederacy. (E2 190–191)

And then Hume continues: “This is plainly the situation of men, with regard to animals; and how far they may be said to possess reason, I leave it to others to determine.”

Earlier I noted that most people seem to hold that we should not kill or hurt the animals unless we have a good reason, but also that any reason except malicious fun is probably good enough. In the same way, Hume’s “laws of humanity” do not clearly forbid us to use the other animals in any way that we might find convenient. We are, after all, as Hume says, stronger than they are, and able to outsmart them. And since we do not need their willing cooperation, and can extort their services, Hume thinks we owe them nothing in return. Although he urges kindness when it is not inconvenient, his view is apparently that when one kind of animal is able to control the others, as human beings are, that is the end of the matter.

Immanuel Kant, by contrast, might seem to have provided the philosophical foundation for the view of the world as an immense resource made for human use. He is perhaps the only philosopher, certainly the most notorious, who says right out that the other animals are mere means, while only human beings are ends in themselves (G 4:428 p. 37; LE 27:458, p. 212).⁷ Yet neither Kant’s own ethical views about how we should treat animals nor the implications of his philosophy are as simple as that would suggest.

Kant’s own ethical views are reported in the records of his course lectures and in his book Metaphysics of Morals. Kant does think we have the right to kill the other animals, but it must be quickly and without pain, and cannot be for the sake of mere sport. He does not say why we should kill them, and the subject of eating them does not come up directly in his discussion, but presumably that is one of the reasons he has in mind. He does not think we should perform painful experiments on nonhuman animals “for the sake of mere speculation, when the end could be also be achieved without these” (MM 6:443, p. 193).⁸ He thinks we may make the other animals work, but not in a way that strains their capacities. The limitation he mentions sounds vaguely as if it were drawn from the Golden Rule: we should only force them to do such work as we must do ourselves (MM 6:443, p. 196). And if they do work for us, he thinks that we should be grateful. In his course lectures, Kant sometimes told a story about the philosopher Leibniz carefully returning a worm he had been studying to its leaf when he was done (LE 27:459, pp. 212–13), thereby expressing his sense of the service the worm had done him. And both in his lectures and in the Metaphysics of Morals, Kant has hard words for people who shoot their horses or dogs when they are no longer useful (MM 6:443, p. 193; LE 27:459, p. 212). Such animals should be treated, Kant insists, “just as if they were members of the household” (MM 6:443, p. 193). He remarks with apparent approval that “in Athens it was punishable to let an aged work-horse starve.”⁹ And he tells us that: “Any action whereby we may torment animals, or let them suffer distress, or otherwise treat them without love, is demeaning to ourselves” (LE 27:710, p. 434).

As that last phrase suggests, however, Kant thinks that these moral duties are not owed to the other animals, but rather to ourselves. He explains:

. . . violent and cruel treatment of animals is. . . intimately opposed to a human being’s duty to himself, and he has a duty to refrain from this; for it dulls his shared feeling of their suffering and so weakens and gradually uproots a natural disposition that is very serviceable to morality in one’s relations with other people. (MM 6:443, p. 193)

In his course lectures, Kant made the same point by saying that nonhuman animals are “analogues” of humanity, and that we therefore “cultivate our duties to humanity” when we practice duties to animals as analogues to human beings (LE 27:459, p. 212).

The position seems nearly incoherent. If human suffering calls forth duties of compassion, duties we are more likely to perform if we are compassionate to animals, why shouldn’t animal suffering call forth duties of compassion as well? If animals are proper objects of gratitude, why don’t we have duties of gratitude toward them? I think this feature of Kant’s view is incoherent, but that the reason why Kant held it is revealing. Kant did not think, as people commonly suppose, that we owe nothing directly to the other animals because they are not ends in themselves. Rather, he thought that they could not be ends in themselves because they cannot place us under obligations. His inference, in other words, is not from the idea that animals are not ends in themselves, to the idea that we do not owe them anything directly. Rather, it is from the idea that they are unable to place us under obligations, to the idea that they are not ends in themselves. In The Metaphysics of Morals, where Kant argues explicitly that human beings can have duties only to other human beings, he says, “. . . a human being has duties only to human beings (himself and others), since his duty to any subject is moral constraint by that subject’s will” (MM 6:442, p. 192). And in the Groundwork of the Metaphysics of Morals, Kant puts the same point this way: “. . . morality is the condition under which alone a rational being can be an end in itself, since only through this is it possible to be a lawgiving member in the Kingdom of Ends” (G 4:435, p. 42). To understand why Kant believes this, we must back up and look in a little more detail at Kant’s view of what makes human beings moral beings.

It is sometimes said that human beings are the only animals who are self-conscious. Animals are aware of the world but not of themselves. Kant mentions this as part of the reason why animals are not ends in themselves (LE 27:458, p. 212). I believe that the issue is much more complicated than that, for self-consciousness, like other attributes, comes in degrees and takes many different forms. A tiger who stands downwind of her intended prey is not merely aware of her prey; she is also locating herself with respect to her prey in physical space, and that shows a rudimentary form of self-consciousness. A social animal who makes gestures of submission when a more dominant animal enters the scene is locating himself in social space, and that too shows a form of self-consciousness. Parallel to these abilities would be a capacity to locate yourself in mental space, to locate yourself with respect to your own thoughts and emotions, and in particular, to know them as your own. This is what we more commonly think of as self-consciousness, a reflective awareness of our mental states as such. Do any of the other animals have this ability to locate themselves in subjective, mental space? Some of the language-trained animals can express the idea “I want”—Koko the gorilla and Alex the African gray parrot, two famous language-trained animals, can both do this—so perhaps they have the ability to think about their own mental states.¹⁰ And some scientists have also pointed to cases of deception to suggest that some animals are aware of the thoughts of others, and therefore, presumably, of their own. The evidence on these questions is perhaps inconclusive.

Early in this essay I mentioned that I believe there is a sharp difference between human beings and the other animals, and this is it. The other animals lead lives that are governed, I believe, by their instincts, desires, emotions, and personal attachments. Because we have the capacity to evaluate the influence of our instincts, desires, emotions, and personal attachments on our actions, we are not completely governed by them. We have the capacity to be governed instead by normative standards and values, by a conception of what we ought to do.¹² We are rational and therefore moral animals, probably the only ones.

This is a big difference. But what immediately follows from this difference is not that we have no duties to the other animals: what follows is most obviously that they have no duties to us, or to one another. Does it follow from that fact that we owe them nothing? Now I come back to the inference I said I was going to explain, Kant’s inference from the fact that the animals cannot place us under obligations to the conclusion that they are not ends in themselves. Kant believed that only beings who can make moral demands on themselves, or can impose laws on themselves, can make moral demands on one another, and therefore that only our fellow rational and moral beings can give us obligations. Each of us regards himself as an end in himself, a being with inherent value, and on that ground demands mutual recognition and respect from those others who are also capable of acting from values and norms. So we only owe obligations to other human beings.

But I don’t think this argument is conclusive. For what it leaves out is that what we demand, when we demand that recognition, is that our natural concerns—the objects of our natural desires and interests and affections—be accorded the status of values, values that must be respected as far as possible by others. And many of those natural concerns—the desire to avoid pain is an obvious example—spring from our animal nature, not from our rational nature. Kant himself believed that the satisfaction of our own natural desires and inclinations should be accorded value, for he believed that we should satisfy them if there is no moral reason against doing so. And that value cannot spring from a demand of moral reason, unless moral reason demands that we respect our own animal as well as our rational nature. The capacity for desire, fear, suffering, and pleasure, after all, is what makes animals “analogues of human beings,— as Kant himself put it, and what in his own argument makes an animal the proper subject of love and gratitude and compassionate treatment. So I might put the point this way: you already believe that it is wrong to make another animal suffer merely for your own ends, since there is an animal—yourself—whose suffering for the ends of others you would declare to be morally objectionable, and a violation of universal law. While it is our rational nature that enables us to value ourselves and one another as ends in ourselves, and to make claims on one another in the name of that value, we make those claims on behalf of our own animal nature as well as of our rational and human nature.¹³ And that means we must acknowledge similar claims on behalf of the other animals. So while Kant is right in thinking that only human beings can place us under obligations, he is wrong in thinking that obligations are owed only to human beings. As rational animals, who place a value on both parts of our own nature, we demand, both of ourselves and one another, that animals should be treated with respect and compassion for their own sakes.

Obviously, elaborating the position I have just sketched into a full theory of how we should treat the other animals would take a good deal of work, both philosophical and empirical. Many people believe that the other animals do not stand in the same relationship to their lives that we stand in to ours, because they are not aware of themselves as beings extended in time, with hopes for the future, plans to carry out, and relationships to develop. This position also ignores the vast variation there is in degrees and kinds of self-consciousness and related properties, such as memory, that we find in the animal world. But perhaps it is true that a human being who loses her life loses something more complex, rich, and connected than a nonhuman animal who loses his life does. On the other hand, a human being and a nonhuman animal who lose their lives both lose everything that they have. There is something imponderable about the comparison.

A human being and another animal who lose their lives both lose everything that they have, unless, as Hume’s character Demea believed, recompense awaits our species in another life, guaranteed by a God who is beneficent to humanity alone. Kant held a position about this that is in some ways similar to Demea’s. For Kant, immortal life is an object of a special epistemic state he calls “practical faith.” A tenet of practical faith is one that meets three conditions: (1) it cannot be proved true, but (2) it also cannot be proved to be false or impossible—both of those because it is beyond the reach of empirical inquiry—and finally (3) unless we believe it we will be subject to moral despair, because we will have to conclude that morality demands the impossible. Because morality commands us with the force of necessity, Kant believed, we are entitled to practical faith in tenets that meet these conditions.

Kant also believed that morality commands us to bring about a state he called “the highest good,” a state in which human beings are happy in proportion to their virtue: in effect, a morally good world. More specifically, Kant thought that we need to believe that such a world will somehow result from our own good conduct. And Kant therefore thought that the existence of God and a future state were tenets of practical faith. Here is his explanation why:

Consider the case of a righteous man . . . who actively reveres the moral law [but] who remains firmly convinced there is no God and . . . no future life. . . . He does not require that complying with the law should bring him an advantage, either in this world or in another; rather, he is unselfish and wants only to bring about the good to which that sacred law directs all his forces. Yet his efforts encounter limits: for while he can expect that nature will now and then cooperate contingently with the purpose that he feels . . . obligated . . . to achieve, he can never expect nature to harmonize with it in a way governed by laws and permanent rules. . . . Deceit, violence, and envy will always be rife around him, even though he himself is honest, peaceable, and benevolent. Moreover as concerns the other righteous people he meets: no matter how worthy of happiness they may be, nature, which pays no attention to that, will still subject them to all the evils of deprivation, disease, and untimely death, just like all the other animals of the earth. And they will stay subjected to these evils always, until one vast tomb engulfs them one and all (honest or not, that makes no difference here) and hurls them, who managed to believe they were the final purpose of creation, back into the abyss of the purposeless chaos of matter from which they were taken. And so this well-meaning person would indeed have to give up as impossible that purpose that the moral law obligated him to have before his eyes. (C3 5:452, p. 341–342; my emphasis)

Unless there is a God and a future state, we have no basis for believing that a morally good world will result from our own good conduct, and therefore we are entitled to have faith that God and a future state exist.¹⁴ But notice that there seem to be two thoughts that Kant thinks we cannot bear to think: first, that our moral conduct will not produce a morally good world, and second, that our fate as a result will be “just like [the fates of] all the other animals of the earth.”

But if we come to believe, as I think we should, that we have duties to the other animals, and that their welfare matters, there is an impact on both of those unbearable thoughts. There is worse to be feared than just that our own fates should be no better than the fates of all the other animals, since as Hume’s character Philo insisted, we cannot think that the goodness of the world depends only on the fate of humanity. A morally good world would be one in which every animal has an existence that is as good as its nature makes possible; it is not enough if human beings are recompensed for their sufferings. But that in turn exacerbates the worry behind the first unbearable thought, that we cannot produce a morally good world by doing the right thing. For we have no coherent vision of a world even remotely like ours, built as it is on a system of predator and prey, in which all animals have good or even comfortable lives, and we certainly cannot hope to produce such a world.

In my own view, the attitude we should have toward the other animals, and our own animal nature, combines elements from Kant’s and Hume’s thought. Kant believed that we need to believe in an ultimate harmony between nature and morality—in effect, in the ultimate goodness of the world—in order to sustain our own moral commitment. I think this is wrong, but I also think it captures something about why it is that so many people, like Hume’s otherwise decent character Cleanthes, simply turn their minds away from the fates of the other animals. Our own moral standards demand that all sentient beings should have comfortable and happy lives, and it is hard to face the fact that we live in a world that is unfriendly to our own moral standards. Still, following Hume, I think we should recognize that our place in nature is just like that of all the other animals in one important way—we are limited in our powers—and therefore we cannot completely impose our own moral standards upon nature. But we are not just animals. So following Kant, we should still try to live up to the moral standards that make us distinctively human, even if we can’t make our world live up to those standards. And those standards, I believe, demand that we treat all animals with compassion and respect, as ends in themselves, not as mere means to our own ends.

Let me end by reminding you that the lecture series for which I wrote this essay was called “Rethinking the Human.” “Humanity” is the name of our species, but it is also a name we give to a particular virtue, the virtue of treating the other animals with kindness. We call societies devoted to the decent treatment of animals “humane societies.” In giving the name of our species to that particular virtue, we make a claim for ourselves, that we are the species that practices the virtue we call “humanity.” Whether we live up to that name is entirely up to us—that is also something that is special about our species. Unlike any other animal, we have a choice about how to live. We can simply be the cleverest of the animals, able to make efficient and profitable use of the others, engaging in only such benevolence as we can easily afford. Or we can be the species that practices the virtue to which we give the name of our species. We can recognize the other animals as fellow creatures, who share our fate, as conscious living beings struggling to get along in a world we never made.

Christine M. Korsgaard is Arthur Kingsley Porter Professor of Philosophy at Harvard University. She is the author of several books about morality, practical reason, and the nature of agency, including The Constitution of Agency and Self- Constitution: Agency, Identity, and Integrity, both forthcoming from Oxford University Press. She is currently working on questions about human/animal relationships. This article was presented on March 5, 2008, at the Center for the Study of World Religions, Harvard Divinity School, as part of its series “Rethinking the Human.”