Suppose we believe that human beings have a right not to be tortured, and the question is raised whether other animals also have this right. How can this issue be investigated? One way is by asking whether there are any differences between humans and nonhumans that would justify us in thinking that humans have the right but that animals don't. If we cannot find any such differences, and if in fact humans and nonhumans are very much alike in the relevant respects—most obviously, in that both can suffer pain, and so both have the same basic interest in not being tortured—then we may conclude, provisionally at least, that nonhumans also have this right.

In the first part of his paper Donald VanDeVeer represents this argument as depending on the assumption that "a being's having an interest in something is a sufficient condition for concluding that it has a right to what is in its interest." But I don't think the argument requires any such assumption. That humans and nonhumans have the same sort of interest in not being tortured is simply an important fact that must be taken into account in assessing the similarities and differences between them. My argument only says that, if there are such important similarities, and there aren't any relevant differences, then human and non-human animals must be in the same boat.

I use the same strategy in arguing that animals have a right to liberty. Now it isn't clear exactly why humans have this right; therefore I consider several possibilities and argue in each case that there is no relevant difference between humans and (at least some) nonhumans. First I consider the view that humans have a right to liberty because liberty is intrinsically good, and individuals have a right not to be deprived of goods which they are capable of enjoying. If that is why humans have the right, then other animals must have it too, since they are also capable of enjoying this intrinsic good. Second, suppose it is thought that humans have a right to liberty because they have interests which are harmed by a loss of freedom, and individuals have a right that their interests not be needlessly harmed. Here I point out that other animals also have interests that suffer when they are deprived of liberty. Third, it has been suggested that liberty has a special importance for humans because humans are moral agents. Against this I argue that some other animals have moral capacities, too.

VanDeVeer objects that in order for my arguments to be successful it must be proved that "creatures with interests thereby have correlative prima facie rights of a sort." But I don't think so. All that is needed for my argument is to show that, for each plausible account of why humans have a right to liberty, a similar account may be provided in the case of other animals. The business about interests is one possible account of why humans have this right; and my point is just that there is no important difference between the human case and the animal case in this respect. As for the business about animals' moral capacities, I don't think there is anything in that argument which even slightly suggests that "only animals exhibiting compassion have rights." The point of that discussion was to show that we cannot cite the moral capacities of humans as a rational basis for ascribing to them rights which we deny to every other creature.

The strategy of argument that I employ is not absolutely conclusive, because it is always possible that with respect to some particular right there are relevant differences between humans and nonhumans that we have overlooked. But this only means that we must be careful. We must compare the characteristics of humans and other animals as carefully as possible, and we must be careful to distinguish the relevant characteristics from the irrelevant ones—bearing in mind that what is relevant in the case of one right may not be relevant in the case of other rights. If we are careful, then I think that the use of this method will bring us as close to the truth as we are likely to get in this area. At the very least, this method of investigating the issue of animal rights will produce more reliable results than arguments based on such dubious generalizations as "only entities that can function as agents and, perhaps, can conceive of forwarding their projects by an exercising of rights could, in fact, have any rights at all."

Nowhere in his paper does VanDeVeer try to show that there are differences between humans and nonhumans relevant to the question of whether animals possess the rights that I discuss. He does suggest that there might be such differences, and I concede that—I simply see no reason to think that there are any. And if there aren't, then we are wrong to deny these rights to animals while claiming them for ourselves.