R.G. Frey (now deceased) was an act utilitarian who: (1) argues against granting rights to animals, (2) denies that nonhuman animals have morally compelling interests, and (3) denies animals “all but the faintest trace of mind” (this quote is from Regan, xxi of the 2004 edition of The Case for Animal Rights). Essentially, he claims that nonhuman animals are capable of experiencing only sensations, such as pains and pleasures. He denies that nonhuman animals are, what Regan refers to as, “subjects-of-a-life”: beings who are not only sentient, but beings who have desires, wants, preferences, beliefs, memory, expectations and so forth. Frey’s claim is that language is a prerequisite for having beliefs and desires, and since nonhuman animals lack language, they do not have beliefs or desires. His well known book, Interests and Rights: The Case Against Animals, describes his position.
Peter Carruthers argues in defense of a Rawlsian version of contractarianism. He argues that since nonhuman animals are not rational beings, they are not protected by the social contract, hence rational human beings have no direct duties to them. In addition, Carruthers endorses a Higher-Order Thought (HOT) theory of consciousness which maintains that in order to have conscious mental states, one must have a higher-order thought about said mental state. He argues that, since nonhuman animals cannot conceptualize their own mental states, they are not phenomenally conscious, i.e., they do not actually experience their mental states, like their mental states of pain (although they can be said to have mental states, like pain).
Carruthers, Peter. 1992. The Animals Issue: Morality in Practice. Cambridge: Cambridge University Press.
Davidson, Donald. 1975. “Thought and Talk.” In Mind and Logic, edited by S. Gutterpan, 7-23. Oxford: Oxford University Press.
Frey, R.G. 1977. “Animal Rights.” Analysis37: 186-9
Frey, R.G. 1980. Interests and Rights: The Case Against Animals. Oxford: The Clarendon Press.
Frey, R.G. 1983 Rights, Killing, and Suffering: Moral Vegetarianism and Applied Ethics. Oxford: Basil Blackwell.
Regan, Tom. 1982. “Frey on Why Animals Cannot Have Simple Desires.” Mind 91: 277-280.