This discussion examines the historical philosophical figures who contributed to the animal rights and welfare movement. Included are the philosophies of Rene Descartes, Immanuel Kant, and John Stuart Mill.
While today several historical philosophical figures have come to play a substantial role in movements for animal rights and welfare, Western philosophy has historically not been very interested in such concerns. Often positioning humans somewhere between the animals and the gods, philosophers, or Western philosophers at least, have historically been more interested in de-emphasizing our relatedness to animals, and emphasizing our proximity to the gods. This has often resulted in some rather troubling views towards animals. Interestingly, though, certain philosophical schools such as Kantianism and utilitarianism have become ideological base-camps for those interested in changing our ethical attitudes and laws regarding animals. This essay will briefly set forward the relevant views of three philosophers who have become important in animal advocacy movements, and discuss the ways in which their work connects to these contemporary movements and contemporary federal law.
II. René Descartes (1596-1650)
For advocates of animal rights and animal welfare, Descartes has become the kicking boy par excellence--and not without good cause. In his philosophical system, Descartes denies animals even the ability to feel pain, and hence whatever small mercies issue consequent to this basic recognition of community. According to Descartes, to feel pain, one must possess a mind.  Animals, according to Descartes, have no mind. “Seeing that a dog is made of flesh you perhaps think that everything which is in you also exists in the dog. But I observe no mind at all in the dog, and hence believe there is nothing to be found in a dog that resembles the things I recognize in a mind.”  Given that animals do not feel pain, vivisection--the practice of cutting animals open while they are still alive--was apparently unproblematic for Descartes, and he has vivid, detached depictions of it in his work. 
Today, happily, there are few who would continue to deny that animals can feel pain. While regulated animal experimentation continues, including the practice of vivisection, current statutory regulations do at least explicitly acknowledge and refer to the fact that animals are capable of feeling pain and distress.  One notable contemporary statutory quirk, however, is that while all animals do feel pain, not all animals are, well, “animals”. Under the Animal Welfare Act , in 7 U.S.C.A. § 2132(g) , some animals are explicitly exempted from the protection offered by the Animal Welfare Act , governing, for instance, vivisection, because in the introductory statutory definition they have been deemed not to be “animals”. The protections offered to animals in the Animal Welfare Act thus afford no protection to them. Such “non-animals” include farm animals, some horses, some rats, some mice, all species of birds, and all cold-blooded animals. The exclusion of rats, mice, and birds was the result of a statutory amendment made as recently as 2002.
While Kantianism has emerged as an ethical back-drop for the animal rights movement, Kant himself certainly did not think that humans owed any ethical duties to animals. While Descartes’ insensitivity to the suffering of animals resulted from his view that animals cannot feel pain, Kant’s emerged from his view that animals do not possesses rationality.  As he writes in his lectures on anthropology: “The fact that man is aware of an ego-concept raises him infinitely above all other creatures living on earth. . . . Because of this, he is a person . . . [h]e is a being who . . . is wholly different from things , such as the irrational animals whom he can master and rule at will.”  Here Kant seems to suggest that the rationality he reserves to persons, that possession by rights of which ethical duties are owed to them, includes some level of self-awareness. Denying that animals have that kind of mental capability, Kant here lumps them together with mere things, saying we can dispose of them as we please. This inordinately harsh-sounding view is somewhat tempered in Kant’s overarching philosophical system, however. While he does not think that one owes any sort of ethical consideration to beasts , he does maintain that cruelty to animals is problematic insofar as it could cultivate a cruel streak—thereby increasing the likelihood that one will behave poorly towards one’s fellow humans.
Kantian philosophy is hence a seemingly unlikely philosophical edifice upon which to erect an animal rights platform. But some animal rights advocates attempt to work within it as there are other aspects of Kantian ethics which they respect, such as the notion that ethical subjects possess inviolable rights. One such advocate, Tom Regan, agrees that a certain level of mental life is required for admission to our ethical community, but argues that Kant’s standard is somewhat amiss, and certainly too rigorous. Redefining the mental criterion, Regan argues that science can play a tremendous role in integrating animals into our ethical community, as science can testify to the significant cognitive abilities of animals and their similarity to our own abilities. 
Another notable animal rights advocate, Steven Wise, all but admits that an animal’s ability to suffer should in-itself be sufficient grounds for receipt of our ethical regard, but continues to focus his advocacy efforts on proving that at least some animals, chimpanzees and bonobos for instance, do possess the Kantian rationality requirement. Wise believes that it is essential to demonstrate this in order to garner for some animals legal personhood , which he ultimately thinks is the best way to ensure ethical treatment of them.  According to Wise, judges, those who are in a position to grant this protective status, are more likely to be swayed by an argument in the Kantian-vein than an argument based on the capacity of animals to feel pain. As Wise writes: “If I were Chief Justice of the Universe, I might make the simpler capacity to suffer, rather than practical autonomy, sufficient for personhood and dignity-rights. For why should even a nonautonomous being be forced to suffer? But the capacity to suffer appears irrelevant to common-law judges in their consideration of who is entitled to basic rights.”  In his works, Wise attempts to gather evidence to meet the highest of Kantian rationality standards. He believes that there is already evidence to show that the cognitive capabilities of chimpanzees and bonobos rise to the level of self-representation that Kant, as seen in the quote above, reserved especially and exclusively for humans--and upon which Kant justified our ethical disregard for animals.
Federal law does seem to recognize that special concessions are owed non-human primates on the basis of their heightened mental abilities, but to date those concessions fall well short of recognition of legal personhood. 7 U.S.C.A. § 2143(a)(2)(B) of the Animal Welfare Act , for instance, has a special provision referring to primates and their psychological needs. According to the Act, standards promulgated for the care of primates should at least mandate that they have “a physical environment adequate to promote the psychological well-being of primates.” 42 U.S.C.A. § 287a-3a , made effective in 2000, establishes another notable, but small realm of special allowances, in establishing a sanctuary for chimpanzees that have been used in medical research but are no longer needed for research.
IV. John Stuart Mill (1806-1873)
While Wise seems to acknowledge that the recognition that animals can suffer and feel pain should be enough to compel us to treat them ethically, he thinks that more can be accomplished by focusing on their rational capabilities. Other animal welfare advocates disagree and make their base-camp within the more animal-friendly philosophy of John Stuart Mill, the famed utilitarian.
Mill holds that “[a]ctions are right in proportion as they tend to promote happiness; wrong as they tend to produce the reverse of happiness. By happiness is intended pleasure and the absence of pain; by unhappiness, pain and the privation of pleasure.”  Straightforwardly then, since animals can feel pain and pleasure (which, unlike Descartes, Mill freely grants), then actions involving causing them pain can be ethically objectionable. Mill ultimately envisions a universe free from pain “secured to all mankind; and not to them only, but, so far as the nature of things admits, to the whole sentient creation”. 
One aspect of utilitarianism that can turn away animal rights advocates and others is that, unlike with Kant’s philosophy, there are no inviolable rights. Bracketing concerns that one might raise against the ethical system as a whole, however, utilitarianism was one of the first Western philosophies to plainly and straightforwardly espouse that animals feel pain and that we cannot ethically disregard them. Animal Liberation by Peter Singer is an excellent illustration of how friendly utilitarianism as an ethical system is towards animal advocacy.
A worry about utilitarianism unique to animal rights and welfare advocates is that compatible with the view that every sentient being’s pain and pleasure counts is the further proposition that humans can experience certain pleasures that count for more than the “animal pleasures”--which can heavily weigh an ethical calculus in favor of humans. Indeed, Mill differentiates between pleasures which only humans can experience and the pleasures which animals can experience, and he proclaims the former higher and more valuable. 
Singer for one argues that this is a very fair distinction which rightly serves to make human life more valuable than an animal’s life. Singer goes on to point out that our problem today is not that animals are suffering to serve some higher human happiness (which might well be ethically defensible), but rather that they are suffering in vast numbers to serve very mundane pleasures, like the pleasure of eating steak and eggs. As he puts it, the problem is that we humans “require the sacrifice of the most important interests of members of other species in order to promote the most trivial interests of our own species.”  Nothing in utilitarianism seems to make allowance for that. Peter Singer’s book accordingly places a special emphasis on such sacrifices, including the plight of animals in factory farms where he finds there to be unnecessary suffering and inadequate regulation. As we noted above, in the Animal Welfare Act farm animals are explicitly excluded from coverage, but there are federal statutes which regulate the transport and slaughter of livestock, including the Humane Methods of Slaughter Act of 1958, 7 U.S.C. §§1901-1906 , and the Twenty-eight Hour Law of 1877, 49 U.S.C. §80502 . Yet, these protections are too minimal, according to Singer, and even so far as they go, they have significant deficiencies. These acts, he contends, are often not well-enforced and contain substantial loopholes. For instance, the Humane Slaughter Act “does not apply to the largest number of animals killed—poultry.” 
While the philosophy of John Stuart Mill does seem particularly hospitable to animals, it is in that regard more the exception than the rule. The finest products of centuries of the Western philosophical tradition, our intellectual gems condensing hundreds of years of rigorous thought and analyticity, all tend to share one common trait—a haste to draw an ethical divide between us and the beasts. Often this divide seems to emerge from some truly baffling philosophical stance, such as the stance that animals cannot feel pain. At such moments one might need to step back from the intellectual posturing of the text, because it might not be the all-mighty intellect that is speaking so emphatically, but rather the very finite flesh. See for instance this passage from Descartes’ Discourse on the Method :
[A]fter the error of those who deny God . . . there is none that leads weak minds further from the straight path of virtue than that of imagining that the souls of the beasts are of the same nature as ours, and hence that after this present life we have nothing to fear or to hope for, any more than flies and ants. But when we know how much the beasts differ from us, we understand . . . that our soul is . . . not bound to die . . . it is immortal. 
In the mind of Descartes, it is not enough to note some similarities and differences between animals and ourselves. We have to erect a decisive divide, we have to refuse to accept that animals could, like us, possess feeling, sensation. We have to completely guard ourselves against their seeming displays of pain. Why? Because to grant that they, like us, could feel, hurt, love, suffer, and yet to watch them live their short, dependent, non-awe-inspiring, and sometimes even tragically pathetic lives would be to face something too horrifying to contemplate—that such might also be our human fate. Descartes bears testimony, as do most of our wizened philosophers, to a simple contemporary psychological truism: we are always most merciless to those who remind us of ourselves.
 “[S]ensations of hunger, thirst, pain and so on are nothing but confused modes of thinking which arise from the union and, as it were, intermingling of the mind with the body.” Descartes, René, Meditations on First Philosophy with Selections from the Objections and Replies , trans. and edited by John Cottingham (Cambridge: Cambridge University Press, 1996), 56. Hence it follows that if an entity possesses no mind to intermingle with the body, then it has no sensations of pain.
 See, for instance, Descartes, René, “Description of the Human Body,” in The Philosophical Writings of Descartes, Volume I , trans. by John Cottingham et al. (Cambridge: Cambridge University Press, 1985), 317.