In his book, Robert Garner brings together political theory and animal rights. He does this by bringing nonhuman animals within the scope of justice. Because Garner takes justice to be that area of morality that is enforceable, the rights of animals thus become a matter for political communities and an issue for which it is legitimate to place constraints on the freedoms of citizens. His project then becomes one of describing ideal circumstances of justice, and of tracing a nonideal path toward this ideal.

Garner begins from the premise that because nonhuman animals have interests, they are worthy of moral concern for their own sakes, and, as a result, they can have rights. The primary interest that he claims is strong enough to place others under a duty is that of not suffering. This interest prohibits the causing of suffering not intended to benefit the animal itself. The interest animals have in not suffering is of equivalent strength to that of humans, and so they have an equal right not to be made to suffer (pp. 101, 128). Whether other animal interests, such as life and liberty, are strong enough to generate rights is something Garner believes is a more open question that he devotes considerable theorizing to answering.

In the end, the author concludes that some animals do have strong interests in life and liberty, but these interests are not strong enough to ground rights. His reason for reaching this conclusion seems to rest upon his conception of rights as “side-constraints” (p. 94). Garner argues that human interests in life and liberty are stronger than those of animals, and so can override them. Because they can be overridden, these interests do not count as rights (p. 133). His argument is not that the interests do not matter morally but that they are not sufficiently weighty to generate rights. Because they matter morally, we ought to take them into consideration, and we ought not sacrifice them readily. Thus, his position rules out most cases of eating animals, since the interest of gaining pleasure from their taste is insufficiently strong to outweigh the vital interest of the animal in not being killed. However, it permits practices that cause death and loss of liberty so long as they do not also cause suffering (p. 123).

Key to Garner’s overarching argument is that the basic interests of nonhuman animals ought to be considered matters of justice and so should be enforced. If nonhuman animals are not owed justice, then respect for their rights is a matter of personal preference. If rights are a matter of preference, then they are not really rights at all. Since respect for the basic interests of nonhuman animals should not be a matter of preference, it follows that they ought to be a matter of justice (p. 59.).

Having established that animal rights are a matter of justice, Garner's purpose is twofold. First, he seeks to describe an ideal theory of justice that includes nonhuman animals within its scope. This ideal theory is intended to meet Rawlsian conditions for a just and stable society compatible with the laws of nature (cf. John Rawls, The Law of Peoples: With “The Idea of Public Reason Revisited” [1999], p, 12). This requires a realistic account of human psychology, taking “men as they are and laws as they might be” (Rousseau, quoted in ibid., p. 7). Transitional steps toward the realistic utopia should not hinder future steps along the path and must themselves be morally permissible (Law of Peoples, p. 89; A John Simmons, “Ideal and Nonideal Theory,” Philosophy & Public Affairs 38 [no. 1, 2010]: 34). In order to count as valid transitional steps, they must also be politically possible (Law of Peoples, p. 89). Second, Garner aims to map out the steps in the nonideal realm that should lead us toward the ideal.

Garner argues that a position ruling out animal suffering, but granting little weight to their life or liberty, is an acceptable transitional step on the route to a realistic utopia. This sentience position ends the most grievous and urgent harms done to animals without hindering progress toward the ideal (p. 135). Because the position allows animals to continue being used for food and scientific procedures, it constitutes an acceptable compromise between animal rights advocates and current norms and attitudes, rendering it achievable. As a result, the sentience position satisfies the conditions of an adequate nonideal theory. This is in contrast to the dominant welfarist paradigm of animal ethics, which holds that suffering, death, and loss of freedom are bad for nonhuman animals but permits them in order to benefit humans. Garner argues that this fails the test of acceptability for a transitional step toward a realistic utopia for two reasons: first, because it is morally impermissible, and second, because it normalizes permissible animal suffering, rendering utopia less likely (p. 91).

There are two broad strands to A Theory of Justice for Animals. The first is a negative case against other ideal theories of animal ethics, and the second is a positive case for the author’s own enhanced sentience position. His consideration of alternative ideal theories is perfunctory and not altogether convincing: he rejects contractualism, capabilities approaches, and utilitarianism in a short 15-page chapter. However, the negative argument is not necessary for his claims to succeed, and the strength of the book lies more in the novelty of the approach taken to argue for his positive claims.

Garner is correct to have recognized that not enough thought has been given in the animal rights literature to either the feasibility of ideal theories advanced or to the steps needed to reach them. Borrowing from the end-state versus transitional stage area of the ideal/nonideal theory literature therefore provides an important and fruitful contribution to the animal rights debate (cf. Laura Valentini, “Ideal vs. Non-Ideal Theory: A Conceptual Map,” Philosophy Compass 7 [no. 9, 2012]: 654–64). However, Garner’s enhanced sentience position is not without problems. The first of these is that it relies upon a conception of rights as near-absolute side-constraints, for which no real argument is offered. Alongside this is an assumption that because the interest in life may be qualitatively different for most humans than it is for animals, it cannot be instantiated in a species-egalitarian way, and therefore nonhuman animals cannot have a right to life. However, it is not clear from Garner's argument why nonhuman animals do not have a right to life in spite of the differences, rather than because of them. Why not, for example, simply grant that nonhuman animals have pro tanto or defeasible rights to life and liberty? The fact that X has a stronger interest in life than Y does not show that Y does not have a right to life. There is no reason to think that two beings might each have a right to life, but that those rights cannot be of different strengths, or that an all-things-considered judgment cannot result in one right being overcome without the other. A second problem is that Garner’s ascription of rights appears to occur at the level of species rather than individuals. At its heart, his thesis is an ethical individualist one. When it comes to rights to life and liberty, Garner’s theoretical commitments should require him to accept that death is a greater harm for some animals than it is for some humans. However, he often slips into species-level theorizing, and his theory ends up being inconsistent because of it.

Overall, the book could have been improved by having more space devoted to the positive arguments within it, and less to the negative ones. However, in spite of this issue, A Theory of Justice for Animals moves the animal rights debate in an important and much-needed political direction, and as such it represents a useful contribution to the literature.