Talks about animal sentience–whether nonhuman animals can feel pain or pleasure–is not a new topic. Currently, we are living in a time when it is not difficult to find documentaries on animal sentience and intelligence, along with alternative products at the supermarket that do not involve animal suffering. The vegan options that we have today have been a long time coming, considering the notion of avoiding animal products for ethical, non-religious reasons has been discussed since Before the Common Era (BCE).


Concern for animal suffering can be found in works by ancient Greek and Roman philosophers. Pythagoras (born circa 569 BCE), the renowned Greek philosopher and mathematician, is the first known ethical vegetarian and animal advocate. In Kerry Walters and Lisa Portmess’ book, Ethical Vegetarianism: From Pythagoras to Peter Singer (1999), the two note that Pythagoras once said, ‘humans must regard all living things as kindred and bestowed on them equal moral consideration’ (pg. 11). He encouraged those who followed him to treat all animals with respect. Unfortunately for Pythagoras and the animals, not everyone who studied his work agreed with his stance on animals. Plato (born circa 428 BCE) and Aristotle (born circa 384 BCE), whose philosophies are largely based on human logic and reason, found animals to be without reason or speech, making them useless unless used and controlled by rational men (Aygün, 2017; Walters & Portmess, 1999). By focusing on humans and proclaiming their distinct rationality, Plato and Aristotle justified animal exploitation.

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There were philosophers from Antiquity who did follow Pythagoras’ approach towards animals, notably Porphyry (born circa 234 CE), who wrote On Abstinence from Eating Food from Animals. He asserted that animals do possess reason; humans are simply unable to understand their language to comprehend it. Roman essayist Plutarch (born circa 46 CE), in his essay ‘On the Eating of Animal Flesh’, similarly proclaimed ‘animals possess characteristics such as intelligence and sentience that entitle them to moral consideration’ (Plutarch quoted in Walters & Portmess, 1999, pg. 12). Stoic philosopher Seneca (born circa 1 BCE) is also known to have advocated for humane, vegetarian lifestyles (Wise, 2000; Walters & Portmess, 1999).

Despite calls by some ancient philosophers to consider animal sentience, Plato’s distinction between rational man and the ‘irrational animal’ took precedence and became the dominant way of thought, leading to nearly a millennium of dormancy in the animal sentience debate. It would only return in the 17th century due to the backlash formed over comments made by Enlightenment thinker René Descartes.

The Enlightenment

René Descartes (born 1596) is best known for his influence during the Enlightenment era. He is widely considered the father of modern philosophy and analytic geometry. His comments on animal sentience, however, made him appear backwards in thought, even to his contemporaries.

Descartes declared that animals do not feel and simply act as machines, or automata (Tauber, 2020; Singer, 1991, Regan, 1983). He compared their functioning to that of a clock–brute matter. He put it, “[w]e have no duties to animals; we have no need for conscience. Whatever intelligence, whatever pain we may seem to see cannot exist in creatures bereft of understanding and feeling” (Descartes quoted in Walters & Portmess, 1999, pg. 255).

While it may appear shocking that a philosopher of such high esteem would hold these views, it aligns directly with his practice of vivisection–the dissection of live animals. He is credited for popularising this practice throughout Europe. It must have made it easier for the philosopher to justify this practice by comforting himself in the assertion that his subjects were unfeeling and unconscious during his experiments, merely squirming due to reflexes. Enlightenment thinker Voltaire (born 1694), outraged by Descartes’ position, posed this to the other philosopher: “Answer me, mechanist, has Nature arranged all the springs of feeling in this animal to the end that he might not feel?” (Voltaire, 1824, pg. 9).

While Descartes’ comments are currently viewed as being preposterous, knowing the scientific consensus today on animal sentience, he did manage to resume the debate after nearly a millennium of dormancy. Utilitarian thinker Jeremy Bentham would emerge a century later, changing the debate significantly.


Jeremy Bentham (born 1748) is known as the originator of classical utilitarianism in modern philosophy. His utilitarianism seeks the ‘greatest happiness’ and views actions as morally right when they produce the ‘most good’ or pleasure, as opposed to pain (Bentham, 2017). Bentham famously applied this to animals when he declared, in An Introduction to the Principles of Morals and Legislation, ‘[t]he question is not Can they reason? or Can they talk? but Can they suffer?’ (Bentham, 2017, pgs. 144). Bentham is the first philosopher recorded to state that an animals’ sentience alone makes them worthy of being spared unnecessary pain, believing their rationality or intelligence to be irrelevant–unlike Plato, Aristotle, and Descartes.

Bentham’s utilitarianism still deems the feelings of one nonhuman animal being worth far less than that of one human, therefore prioritising human welfare. For example, his theory defends raising and killing animals for food—something we cannot fathom how torturous and painful it must be for the animals—to satiate one person who, in most situations, has other things to eat. Despite flaws in Bentham’s theory for the animal protection movement, he is still credited for considering animals’ sentience as the only important criteria for them to be protected and inspired others with his statement.

Modern Utilitarianism, Animal Welfare, and Animal Rights

Come the 20th century, the animal protection movement is at its height, though having split due to welfarist and rights stances. This final section will focus on the contributions to animal sentience and vegan discourses by animal welfarist and utilitarian Peter Singer, rights activist Tom Regan, critical animal studies and feminist writer Carol J. Adams, and legal scholar and founder of the Nonhuman Rights Project, Steven Wise.


Peter Singer was born nearly 200 years after Jeremy Bentham. Despite about two centuries of separation, Singer is highly influenced by Bentham’s utilitarianism. They both believe that one sentient being counts as one individual and preventing the majority of those individuals’ pain is the ultimate goal, alluding to egalitarianism (Bentham, 2017; Singer, 1991). While Bentham’s utilitarianism says it is acceptable to use animals for human means when producing any human benefit, Singer believes that pain is pain for any sentient being, therefore meaning their interests should be considered equally. It is for this reason that Singer supports a vegetarian lifestyle, while Bentham did not. Singer’s book Animal Liberation (1975) popularised Richard Ryder’s coined term speciesism, which is discrimination and/or exploitation of nonhuman animal species by humans, based on the belief of human superiority (Bekoff, 2010).

Singer’s welfarism advocates for an increase in animal well-being until their untimely death. It should be noted that Singer distinguishes between animals’ higher and lower mental capabilities, which is contradictory to his original claim that all ‘pain is pain’. Singer notes the species that he deems worthy of equal consideration through his ‘preference utilitarianism’, considering those less worthy of moral consideration as the ones without the ability to think forward, visualize a future, and possess the desire to go on living (Paccagnella & Marchetto, 2019; Singer, 1991; Regan, 1983). This results in Singer to claim that animals such as humans, apes, whales, dolphins, pigs, monkeys, birds, and octopuses—having high mental capabilities and the ability to foresee their death—are more unacceptable to kill than other ‘less intelligent’ animals (Kniess, 2019; Paccagnella & Marchetto, 2019; Regan, 1983). Despite Singer’s preference utilitarianism, he is an advocate for the increased welfare of all animals when possible, indifferent to their mental capabilities (Singer, 1991).

According to rights philosophers and vegan advocates such as Tom Regan, there are aspects of Singer’s animal welfare position that are problematic from the animal rights perspective. Singer still accepts the property status of animals and does not believe in granting animals rights and thus liberation in the sense that Regan and Wise do.


In Tom Regan’s Case for Animal Rights (1983), the animal rights scholar argues that an animal’s intelligence is not justification for them to be spared or not. Regan finds animals of ‘lesser intelligence’ to be that much more worthy of protection by us ‘rational agents’, given the former’s innocence. He believes that we should not abuse these animals just because it is simply easier to get away with it. Regan does not utilize utilitarianism in his stance, but rather sees the suffering of any ‘subjects-of-a-life,’ or any living being, to be immoral, with their killing almost never justifiable (except in instances of self-defence) (Regan, 1983). As an animal rights advocate, Regan believes in the inherent worth of animals and their right to life, while Bentham and Singer consider the treatment of animals while they are alive, or their welfare, as more important than their ultimate end (Bentham, 2017; Singer, 1991; Regan, 1983). Regan argues that it is the killing of food animals that is wrong, not just the pain that they experience leading up to their unnatural deaths. Regan believes that if humans have a natural right to live, animals do as well.


Carol J. Adams is a vegan and feminist advocate. In her famous work The Sexual Politics of Meat: A Feminist-Vegetarian Critical Theory, Adams points out the intersectional objectification of human and nonhuman females (1990). For example, dairy cows’ reproductive systems are routinely exploited and subjected to artificial insemination by producers, as cows, like all mammals, must be pregnant in order to produce milk.

As dairy producers are concerned with making profits and therefore human consumption of milk, a cow’s calves are not allowed to drink her milk, leading to their immediate separation–the shock of which is known to leave both mothers and calves to cry for days (Geer, 2020). Adams goes beyond mainstream feminist theory literature by pointing out the intersectional bond between mother and child that transcends species. Adams is giving a voice to animals who are exploited in the meat and dairy industries and is a trailblazer for promoting their rights from a feminist perspective.


The final contributor to the animal rights dialogue that will be discussed is Steven Wise. Wise is a law professor, animal rights legal scholar, and the founder of the Nonhuman Rights Project. His focus on animal intelligence in Rattling the Cage (2000) suggests that the current legal status of animals is what makes their mistreatment so easy to get away with—which is why he promotes ‘legal personhood’ for some high functioning mammals, including great apes, elephants, dolphins, and whales (Tauber, 2020; Wise, 2000). Wise believes that animals have the right not to be treated as things, which can only be enforced by changes in the law.

Wise’s legal initiatives at the Nonhuman Rights Project can change the way humans will view and treat animals in the future. His work, alongside that of Regan, calls for altering the status quo that allows animal oppression and injustices to take place without question.

In May 2021, the New York Court of Appeals finally, after many failed attempts by Wise, agreed to hear a case on ‘Happy’ the elephant, who has been captive in the Bronx Zoo for over 40 years (Fonrouge, 2021). Happy finally has a chance to live happily at a sanctuary, as the Nonhuman Rights Project is hopeful for, as a result of the unprecedented acceptance of her case.

In sum…

The animal protection debate is not a new phenomenon. It was not uncommon for philosophers during Antiquity to avoid eating animal products for ethical reasons. Those of the Enlightenment age and centuries to come made statements that renewed the debate. By the 20th century, the animal protection movement divided into welfarist and rights activism as more philosophers and scholars began taking specific stances on the plight of nonhuman animals. Today, we can easily turn on any streaming service and watch a plethora of documentaries stating the ethical, environmental, and health reasons for following a vegan lifestyle. Had it not been for the work laid out by those like Pythagoras, Bentham, and Regan, perhaps we would not be living in the vegan-friendly 2022 world that is currently available to us.

Written by: Vivian Sandler
Vegan Content Manager, IAPWA


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