The usual manner of justifying the claim that animals are not equal to human beings is to point out that only humans have some property, and then argue that that property is what confers a full and equal moral status to human beings. Some philosophers have used the following claims on this strategy: (1) only human beings have rights; (2) only human beings are rational, autonomous, and self-conscious; (3) only human beings are able to act morally; and (4) only human beings are part of the moral community.
On one common understanding of rights, only human beings have rights. On this conception of rights, if a being has a right then others have a duty to refrain from infringing that right; rights entail duties. An individual that has a right to something must be able to claim that thing for himself, where this entails being able to represent himself in his pursuit of the thing as a being that is legitimately pursuing the furtherance of his interests (Cf. McCloskey, 1979). Since animals are not capable of representing themselves in this way, they cannot have rights.
However, lacking rights does not entail lacking direct moral status; although rights entail duties it does not follow that duties entail rights. So although animals may have no rights, we may still have duties to them. The significance of having a right, however, is that rights act as “trumps” against the pursuit of utility. In other words, if an individual has a right to something, we are not permitted to infringe on that right simply because doing so will have better overall results. Our duties to those without rights can be trumped by considerations of the overall good. Although I have a duty to refrain from destroying your property, that duty can be trumped if I must destroy the property in order to save a life. Likewise, I am not permitted to harm animals without good reason; however, if greater overall results will come about from such harm, then it is justified to harm animals. This sort of reasoning has been used to justify such practices as experimentation that uses animals, raising animals for food, and using animals for our entertainment in such places as rodeos and zoos.
There are two points of contention with the above account of rights. First, it has been claimed that if human beings have rights, then animals will likewise have rights. For example, Joel Feinberg has argued that all is required in order for a being to have a right is that the being be capable of being represented as legitimately pursuing the furtherance of its interests (Feinberg, 1974). The claim that the being must be able to represent itself is too strong, thinks Feinberg, for such a requirement will exclude infants, the senile, and other marginal cases from the class of beings with rights. In other words, Feinberg invokes yet another instance of the Argument from Marginal Cases in order to support his position.
Second, it has been claimed that the very idea of rights needs to be jettisoned. There are two reasons for this. First, philosophers such as R. G. Frey have questioned the legitimacy of the very idea of rights, echoing Bentham’s famous claim that rights are “nonsense on stilts” (Frey, 1980). Second, philosophers have argued that whether or not a being will have rights will depend essentially on whether or not it has some other lower-order property. For example, on the above conception of rights, whether a being will have a right or not will depend on whether it is able to represent itself as a being that is legitimately pursuing the furtherance of its interests. If that is what grounds rights, then what is needed is a discussion of the moral importance of that ability, along with a defense of the claim that it is an ability that animals lack. More generally, it has been argued that if we wish to deny animals rights and claim that only human beings have them, then we must focus not so much on rights, but rather on what grounds them. For this reason, much of the recent literature concerning animals and ethics focuses not so much on rights, but rather on whether or not animals have certain other properties, and whether the possession of those properties is a necessary condition for equal consideration (Cf. DeGrazia, 1999).
Some people argue that only rational, autonomous, and self-conscious beings deserve full and equal moral status; since only human beings are rational, autonomous, and self-conscious, it follows that only human beings deserve full and equal moral status. Once again, it is not claimed that we can do whatever we like to animals; rather, the fact that animals are sentient gives us reason to avoid causing them unnecessary pain and suffering. However, when the interests of animals and human beings conflict we are required to give greater weight to the interests of human beings. This also has been used to justify such practices as experimentation on animals, raising animals for food, and using animals in such places as zoos and rodeos.
The attributes of rationality, autonomy, and self-consciousness confer a full and equal moral status to those that possess them because these beings are the only ones capable of attaining certain values and goods; these values and goods are of a kind that outweigh the kinds of values and goods that non-rational, non-autonomous, and non-self-conscious beings are capable of attaining. For example, in order to achieve the kind of dignity and self-respect that human beings have, a being must be able to conceive of itself as one among many, and must be able to choose his actions rather than be led by blind instinct (Cf. Francis and Norman, 1978; Steinbock, 1978). Furthermore, the values of appreciating art, literature, and the goods that come with deep personal relationships all require one to be rational, autonomous, and self-conscious. These values, and others like them, are the highest values to us; they are what make our lives worth living. As John Stuart Mill wrote, “Few human creatures would consent to be changed into any of the lower animals for a promise of the fullest allowance of a beast’s pleasures” (Mill, 1979). We find the lives of beings that can experience these goods to be more valuable, and hence deserving of more protection, than the lives of beings that cannot.
Another reason for giving stronger preference to the interests of human beings is that only human beings can act morally. This is considered to be important because beings that can act morally are required to sacrifice their interests for the sake of others. It follows that those that do sacrifice their good for the sake of others are owed greater concern from those that benefit from such sacrifices. Since animals cannot act morally, they will not sacrifice their own good for the sake of others, but will rather pursue their good even at the expense of others. That is why human beings should give the interests of other human beings greater weight than they do the interests of animals.