Rawls is clear in A Theory of Justice that the basis of equality does not extend to nonhuman animals (hereafter: animals). This is because they are not moral persons with the two basic moral powers: the ability to develop a conception of the good and a sense of justice or the right. Strictly speaking, equal justice applies only to those with these two powers. Hence animals are left out of Rawls’s famous social contract experiment. Another way to put the point is to say that it is those who can give justice who are owed justice (TJ 15, 441–449; also LP 92, 171).

In an earlier piece, “The Sense of Justice” (1963), Rawls asked the question, “who is owed justice?” His response was that the capacity to be just was a necessary and suficient condition for receiving justice. He admits that establishing that the capacity to be just is a necessary condition for receiving justice is much more difficult than it is to establish that the capacity to be just is a suficient condition for receiving justice. (In TJ Rawls is not explicit that the two moral powers are necessary for being owed justice, only that they are suficient for being owed justice, although the necessary condition may be implied in TJ.) Nonetheless he concludes that we have no duty of justice to animals, as there might be in utilitarianism where possession of sentiency seems to be a suficient condition for being a full subject of rights (CP 112–116).