My argument in this section turns on considerations about the natural "right to life" that we humans are sometimes said uniquely to possess, and to possess to an equal degree. My strategy here will be similar to my strategy in the previous section. What I will try to show is that arguments that might be used in defense of the claim that all human beings have this natural right, to an equal extent, would also show that animals are possessors of it, whereas arguments that might be used to show that animals do not have this right would also show that not all human beings do either. Just as in the preceding section, however, so here too, a disclaimer to completeness is in order. I have not been able to consider all the arguments that might be advanced in this context; all that I have been able to do is consider what I think are the most important ones.

Let us begin, then, with the idea that all humans possess an equal natural right to life. And let us notice, once again, that it is an equal natural right that we are speaking of, one that we cannot acquire or have granted to us, and one that we all are supposed to have just because we are human beings. On what basis, then, might it be alleged that all and only human beings possess this right to an equal extent? Well, a number of familiar possibilities come immediately to mind. It might be argued that all and only human beings have an equal right to life because either (a) all and only human beings have the capacity to reason, or (b) all and only human beings have the capacity to make free choices, or (c) all and only human beings have a concept of "self," or (d) all and only human beings have all or some combination of the previously mentioned capacities. And it is easy to imagine how someone might argue that, since animals do not have any of these capacities, they do not possess a right to life, least of all one that is equal to the one possessed by humans.

I have already touched upon some of the difficulties such views must inevitably encounter. Briefly, it is not clear, first, that no nonhuman animals satisfy any one (or all) of these conditions, and, second, it is reasonably clear that not all human beings satisfy them. The severely mentally feeble, for example, fail to satisfy them. Accordingly, we want to insist that they have a right to life, then we cannot also maintain that they have it because they satisfy one or another of these conditions. Thus, if we want to insist that they have an equal right to life, despite their failure to satisfy these conditions, we cannot consistently maintain that animals, because they fail to satisfy these conditions, therefore lack this right.

Another possible ground is that of sentience, by which I understand the capacity to experience pleasure and pain. But this view, too, must encounter a familiar difficulty—namely, that it could not justify restricting the right only to human beings.

What clearly is needed, then, if we are to present any plausible argument for the view that all and only human beings have an equal natural right to life, is a basis for this right that is invariant and equal in the case of all human beings and only in their case. It is against this backdrop, I think, that the following view naturally arises.[1] This is the view that the life of every human being has "intrinsic worth—that, in Kant's terms, each of us exists as "an end in himself"—and that this intrinsic worth which belongs only to human beings, is shared equally by all. "Thus," it might be alleged, "it is because of the equal intrinsic worth of all human beings that we all have an equal right to life."

This view, I think, has a degree of plausibility which those previously discussed lack. For by saying that the worth that is supposed to attach to a being just because he or she is human is intrinsic, and that it is because of this that we all have an equal natural right to life, this view rules out the possibility that one human being might give this right to or withhold it from another. It would appear, therefore, that this view could make sense of the alleged naturalness of the right in question. Moreover, by resting the equal right to life on the idea of the equal intrinsic worth of all human beings, this view may succeed, where the others have failed, in accounting for the alleged equality of this right.

Despite these apparent advantages, however, "the view under consideration must face certain difficulties. One difficulty lies in specifying just what it is supposed to mean to say that the life of every human being is "intrinsically worthwhile."[2] Now, it cannot mean that "each and every human being has a natural right to life." For the idea that the life of each and every human being has intrinsic worth was introduced in the first place to provide a basis for saying that each and every human being has an equal right to life. Accordingly, if, say, "Jones's life is intrinsically worthwhile" ends up meaning "Jones has an equal right to life," then the claim that the life of each and every individual is equally worthwhile, judged intrinsically, cannot be construed as a basis for saying that each and every human being has an equal right to life. For the two claims would mean the same thing, and one claim can never be construed as being the basis for another, if they both mean the same.

But a second and, for our purposes, more important difficulty is this: On what grounds is it being alleged that each and every human being, and only human beings, are intrinsically worthwhile? Just what is there, in other words, about being human, and only about being human, that underlies this ascription of unique worth? Well, one possible answer here is that there isn't "anything" that underlies this worth. The worth in question, in short, just belongs to anyone who is human, and only to those who are. It is a worth that we simply recognize or intuit, whenever we carefully examine that complex of ideas we have before our minds when we think of the idea, "human being." I find this view unsatisfactory, both because it would seem to commit us to an ontology of value that is very difficult to defend, and because I, for one, even after the most scrupulous examination I can manage, fail to intuit the unique worth in question. I do not know how to prove that the view in question is mistaken in a few swift strokes, however. All I can do is point out the historic precedents of certain groups of human beings who have claimed to "intuit" a special worth belonging to their group and not to others within the human family, and say that it is good to remember that alluding to a special, intuitive way of "knowing" such things could only serve the purpose of giving an air of intellectual respectability to unreasoned prejudices. And, further, I can only register here my own suspicion that the same is true in this case, though to a much wider extent. For I think that falling into talk about the "intuition of the unique intrinsic worth of being human" would be the last recourse of men who, having found no good reason to believe that human beings have a unique intrinsic worth, would go on believing that they do anyhow.

Short of having recourse to intuition, then, we can expect those who believe that human beings uniquely possess intrinsic worth to tell us what there is about being human, in virtue of which this worth is possessed. The difficulty here, however, as can be anticipated, is that some familiar problems are going to raise their tiresome heads. For shall we say that it is the fact that humans can speak, or reason, or make free choices, or form a concept of their own identity that underlies this worth? These suggestions will not work here, anymore than they have before. For there are some beings who are human who cannot do these things, and there very well may be some beings who are not human who can. None of these capacities, therefore, could do the job of providing the basis for a kind of worth that all humans and only humans are supposed to possess.

But suppose we try to unpack this notion of intrinsic worth in a slightly different way.[3] Suppose we say that the reasons we have for saying that all and only human beings exist as ends in themselves are, first, that every human being has various positive interests, such as desires, goals, hopes, preferences and the like, the satisfaction or realization of which brings intrinsic value to their lives, in the form of intrinsically valuable experiences; and, second, that the intrinsic value brought to the life of any one man, by the satisfaction of his desires or the realization of his goals, is just as good, judged in itself, as the intrinsic value brought to the life of any other man by the satisfaction or realization of those comparable desires and goals he happens to have. In this sense, then, all men are equal, and it is because of this equality among all men, it might be alleged, that each man has as much right as any other to seek to satisfy his desires and realize his goals, so long, at least, that, in doing so, he does not violate the rights of any other human being. "Now, since," this line of argument continues, "no one can seek to satisfy his desires or realize his goals if he is dead, and in view of the fact that every man has as much right as any other to seek to satisfy his desires and realize his goals, then to take the life of any human being will always be prima facie to violate a right which he shares equally with all other human beings—namely, his right to life."

What shall we make of this argument? I am uncertain whether it can withstand careful scrutiny. Whether it can or not, however, is not a matter I feel compelled to try to decide here. What I do want to point out is, of the arguments considered here, this one has a degree of plausibility the others lack, not only because, as I have already remarked, it addresses itself both to the alleged naturalness and the alleged equality of the right in question, but also because it rests on what I take to be a necessary condition of being human — namely, that a being must have interests. For these reasons, then, I do not think I can be accused of "straw-man" tactics by choosing this as the most plausible among a cluster of possible arguments that might be urged in support of the contention that all human beings have an equal natural right to life. At the same time, however, as can be anticipated, I believe that, whatever plausibility this argument might have in this connection, it would also have in connection with the claim that animals, too, have an equal natural right to life.

For even if it is true that this argument provides us with adequate grounds for ascribing a natural right to life equally to all human beings, there is nothing in it that could tend to show that this is a right that belongs only to those beings who are human. On the contrary, the argument in question would equally well support the claim that any being who has positive interests which, when satisfied, bring about experiences that are just as intrinsically valuable as the satisfaction of the comparable interests of any other individual, would have an equal right to life. In particular, then, it would support the view that animals have an equal right to life, if they meet the conditions in question. And a case can be made for the view that they do. For, once again, it seems clear that animals have positive interests, the satisfaction or realization of which would appear to be just as intrinsically worthwhile, judged in themselves, as the satisfaction or realization of any comparable interest a human being might have. True, the interests animals have may be of a comparatively low grade, when we compare them to, say, the contemplative interests of Aristotle's virtuous man. But the same is true of many human beings : their interests may be largely restricted to food and drink, with occasional bursts of sympathy for a few. Yet we would not say that such a man has less of a right to life than another, assuming that all men have an equal right to life. Neither, then, can we say that animals, because of their "base" interests, have any less of a right to life.

One way to avoid this conclusion ... is to deny that animals have interests.[4] But on what basis might this denial rest? A by now familiar basis is that animals cannot speak; they cannot use words to formulate or express anything; thus, they cannot have an interest in anything. But this objection obviously assumes that only those beings who are able to use words to formulate or express something can have interests, and this, even ignoring the possibility that at least some animals might be able to do this, seems implausible. For we do not suppose that infants, for example, have to learn to use a language before they can have any interests. Moreover, the behavior of animals certainly seems to attest to the fact that they not only can, but that they actually do have interests. Their behavior presents us with many cases of preferential choice and goal-directed action, in the face of which, and in the absence of any rationally compelling argument to the contrary, it seems both arbitrary and prejudicial to deny the presence of interests in them.

The most plausible argument for the view that humans have an equal natural right to life, therefore, seems to provide an equally plausible justification for the view that animals have this right also. But just as in saying that men and animals have an equal right to be spared undeserved pain, so here, too, we would not imply that the right in question can never be overridden. For there may arise circumstances in which an individual's right to life could be outweighed by other, more pressing moral demands, and where, therefore, we would be justified in taking the life of the individual in question. But even a moment's reflection will reveal that we would not condone a practice which involved the routine slaughter of human beings simply on the grounds that it brought about this or that amount of pleasure, or this or that amount of intrinsically good experiences for others, no matter how great the amount of good hypothesized. For to take the lives of individuals, for this reason, is manifestly not to recognize that their life is just as worthwhile as anybody else's, or that they have just as much right to life as others do. Nor need any of this involve considerations about the amount of pain that is caused the persons whose lives are taken. Let us suppose that these persons are killed painlessly; that still would not alter the fact that they have been treated wrongly and that the practice in question is immoral. If, then, the argument in the present section is sound; and assuming that no other basis is forthcoming which would support the view that humans do, but animals do not, have an equal right to life; then the same is true of any practice involving the slaughter of animals, and we have, therefore, grounds for responding to the two objections raised, but not answered, at the end of the first section. These objections were, first, that since the only thing wrong with the way animals are treated in the course of being raised and slaughtered is that they are caused a lot of undeserved pain, the thing to do is to desensitize them so that they don't feel anything. What we can see now, however, is that the undeserved pain animals feel is not the only morally relevant consideration; it is also the fact that they are killed that must be taken into account.

Similarly, to attempt to avoid the force of my argument for conditional vegetarianism by buying meat from farms that do not practice intensive rearing methods or by hunting and killing animals oneself— expedients that formed the basis of the second objection at the end of Section I—these expedients will not meet the total challenge vegetarians can place before their meat-eating friends. For the animals slaughtered on even the most otherwise idyllic farms, as well as those shot in the wild, are just as much killed, and just as much dead, as the animals slaughtered under the most ruthless of conditions.

Unless or until, then, we are given a rationally compelling argument that shows that all and only human beings have an equal right to life; and so long as any plausible argument that might be advanced to support the view that all human beings have this right can be shown to support, to the same extent, the view that animals have this right also; and so long as we believe we are rationally justified in ascribing this right to humans and to make reference to it in the course of justifying our judgment that it is wrong to kill a given number of human beings simply for the sake of bringing about this or that amount of good for this or that number of people; given all these conditions, then, I believe we are equally committed to the view that we cannot be justified in killing any one or any number of animals for the intrinsic good their deaths may bring to us. I do not say that there are no possible circumstances in which we would be justified in killing them. What I do say is that we cannot justify doing so in their case, anymore than we can in the case of the slaughter of human beings, by arguing that such a practice brings about intrinsically valuable experiences for others.

Once again, therefore, the onus of justification lies, not on the shoulders of those who are vegetarians, but on the shoulders of those who are not. If the argument of the present section is sound, it is the nonvegetarian who must show us how he can be justified in eating meat, when he knows that, in order to do so, an animal has had to be killed. It is the nonvegetarian who must show us how his manner of life does not contribute to practices which systematically ignore the right to life which animals possess, if humans are supposed to possess it on the basis of the most plausible argument considered here. And it is the nonvegetarian who must do all this while being fully cognizant of the fact that he cannot defend his way of life merely by summing up the intrinsic goods— the delicious taste of meat, for example—that come into being as a result of the slaughter of animals.

This is not to say that practices that involve taking the lives of animals cannot possibly be justified. In some cases, perhaps, they can be, and the grounds on which we might rest such a justification would, I think, parallel those outlined in the preceding section in connection with the discussion of when we might be morally justified in approving a practice that caused animals nontrivial, undeserved pain. What we would have to show in the present case, I think, in order seriously to consider approving of such a practice, is (1) that such a practice would prevent, reduce, or eliminate a much greater amount of evil, including the evil that attaches to the taking of the life of a being who has as much claim as any other to an equal natural right to life; (2) that, realistically speaking, there is no other way to bring about these consequences; and (3) that we have very good reason to believe that these consequences will, in fact, obtain. Now, perhaps there are some cases in which these conditions are satisfied. For example, perhaps they are satisfied in the case of the Eskimo's killing of animals and in the case of having a restricted hunting season for such animals as deer. But to say that this is (or may be) true of some cases is not to say that it is true of all, and it will remain the task of the nonvegetarian to show that what is true in these cases, assuming that it is true, is also true of any practice that involves killing animals which, by his actions, he supports.