Early Philosophy


Modern animal rights emerged as a philosophical concept in the late 17th century, and was a product of the enlightenment period. Prior to this, animals were frequently regarded in both western religion and philosophy as automatons; mechanized creatures, incapable of experiencing pleasure, pain or consciousness. However, it should be noted that some ancient philosophers and religious scholars acknowledged animal sentience. For example, the Greek philosopher Theophratus, a student of Aristotle, believed that animals were capable of reasoning, and Pythagoras believed that human and nonhuman souls were the same matter, capable of cross-reincarnation.

The early enlightenment philosophers believed that all rational beings should strive to avoid causing pain or injury to non-human animals. This was founded on the belief that whilst not all creatures are rational, all creatures are sentient, and all sentient creatures should be protected from wanton and unnecessary ill treatment.

Jean-Jacques Rousseau (1712-1778) wrote extensively on this topic, and based his philosophy on the principle of compassion and sentience based rights. He argued that the creature capable of experiencing pleasure and suffering was entitled to rights, in particular the right to be free from unnecessary suffering and harm.

The philosopher and lexicographer Samuel Johnson (1709-1784) also advocated animal rights, and based his conclusions on the principle of sentience. As a pamphleteer, he wrote extensively against the use of medical testing.

Whilst it may appear a simple principle to the modern reader, the principle of sentience-based animal rights was revolutionary at its time. Indeed, it remains important. Not only did sentience-based rights inspire later philosophers and animal rights advocates, but it continues to form the basis of modern arguments promoting the protection of the rights of non-human animals.

Further Reading
  • Discourse on Inequality by Jean-Jacques Rousseau
  • Animal Rights and Moral Philosophy by Julian H. Franklin
  • Romanticism and Animal Rights by David Perkins
  • Animal Rights: A Historical Anthology by Andrew Linzey
  • Of the Reason of Animals’ by David Hume
  • 'The Language of Animals' by Michel de Montaigne

Utilitarianism and Animal Rights

Jeremy Bentham

Jeremy Bentham (1748-1832) also contributed to the philosophy of animal rights. He argued that his philosophy of utilitarianism demanded greater rights for non-human animals. The consequentialist philosophy of utilitarianism argues that the moral value of an action is determined by its outcome. The goal should be to ensure that an action achieves, “the greatest happiness for the greatest number”.

Based in part on the principle of sentience, Bentham argued that because animals are capable of happiness and suffering, their wellbeing is relevant when considering whether an action achieves happiness for the greatest number. He argued that non-human animals should not be excluded from the utilitarian calculation. In Introduction to the Principles of Morals and Legislation (1823), Bentham famously declared: “The questions is not ‘can they reason?’ Nor, ‘can they talk?’ But rather, it is ‘Can they suffer?’

Further Reading

The 18th Century

The Rise of Anti-Cruelty Movements

The animal rights movement garnered considerable support during the 18th century. The philosophy of sentience based rights gained support, and during the course of the century, a series of laws were passed aimed at protecting animals from cruelty. This included the Cruel Treatment of Cattle Act 1822 and the Animals Act 1835. The former made it an offence to, “beat, abuse or ill treat any horse, mare, gelding, mule, ass, ox, cow, heifer, steer, sheep or other cattle”. The latter extended the 1822 act to cover bulls, dogs, bear and sheep. It also prohibited bear baiting and cockfighting.

In addition to new laws, new societies were founded, including the RSPCA (1824), the American Society for the Prevention of Cruelty to Animals (1866), the American Humane Association (1877), the Royal Society for the Protection of Birds (1889) and the National Anti-Vivisection Society (1875). These societies campaigned tirelessly to improve the quality of life for non-human animals.

During this period, philosophers, writers, poets and scientists voiced their support for animal rights, including Leo Tolstoy (1828-1910), Mark Twain (1835-1910) and Charles Darwin (1809-1882). Their arguments were based on the principles set out by earlier philosophers, and were rooted in the belief that sentient, non-human animals should be protected from cruelty.

Darwin’s support for animal rights was based on his theory of evolution. He concluded, “There is no fundamental difference between man and the higher animals in their mental faculties…The lower animals, like man, manifestly feel pleasure and pain, happiness and misery.” He argued that non-human animals are to be regarded as our cousins, capable of feeling pain and emotions, and therefore deserving of legal protection.

Leo Tolstoy wrote extensively about animal rights and the protection of animals from human cruelty. He was a committed vegetarian and wrote extensively about the cruelty of slaughterhouses. His beliefs were also based deeply on his own religious views. He wrote, “’Thou shalt not kill’ does not apply to murder of one’s own kind only, but to all living beings; and this Commandment was inscribed in the human breast long before it was proclaimed from Sinai.” He further observed, “As long as there are slaughterhouses, there will be battlefields.”

Mark Twain was a keen supporter of animal rights, and he wrote repeatedly and critically against many issues, including vivisection and blood sports. He based his views both on Darwinism and the belief that animals, whilst not necessarily rational, were sentient. He argued that humans were the only animals to deliberately and maliciously cause pain to others. Indeed, he devoted a book to the topic; Man’s Place in the Animal World, in which he wrote:

“The difference between an earl and an anaconda is, that the earl is cruel and the anaconda isn't; and that the earl wantonly destroys what he has no use for, but the anaconda doesn't. This seemed to suggest that the earl was descended from the anaconda, and had lost a good deal in the transition.”

It is clear that during the 18th Century, there was a dramatic rise in anti-cruelty laws, and these laws were based on the protection of sentient non-humans from cruelty and needless suffering. These developments arose from the work of earlier philosophers, including Bentham, and social activists and public figures.

Further Reading

20th Century Principles

Animal Liberation and Speciesism

The post-industrial age produced an enormous increase in factory farming and intensive farming methods. As a result, an enormous number of farm animals were exposed to large-scale abuse. Similarly, there was a dramatic rise in vivisection.

The industrialization of cruelty triggered the formation of anti-exploitation groups. The most well known group was the Oxford Group, which was formed in the 1960s by a group of intellectuals who opposed animal exploitation. The movement moved away from simply opposing cruelty on the basis of sentience and began to rely on the philosophy of equality. Inspired by other civil rights movements of the period, including the feminist movement and the earlier anti-segregation movement, the Oxford Group aimed to rely on the philosophy of equality to extend rights to animals.

In 1964, Ruth Harrison published Animal Machines, her scathing attack on intensive factory farming and the cruelty inflicted on animals. The philosophical principle of speciesism emerged at the same time. Psychologist Richard Ryder defined the term as, “to describe the widespread discrimination that is practiced by man against other species. Speciesism is racism, and both overlook and underestimate the similarities between the discriminator and those discriminated against.”

The ideas that emerged from the early Speciesism groups developed into the Animal Liberation movement. In 1975, philosopher Peter Singer wrote Animal Liberation, which had a formative effect on the new wave of assertive, grass roots animal rights movements. Singer based his argument on utilitarianism and argued that the goal of society should be to maximize the greatest good for the greatest number. This included considering non-human animals.

Relying on the principle of “Speciesism”, Singer argued that to exclude non-human animals from any utilitarian calculation was unjustifiable and discriminatory. Society should strive to regard all sentient beings as equal. He argued that just as it would be wrong to minimize the importance of developmentally challenged people or other minorities on the basis that they lacked full rational thought, it would be wrong to minimize the importance of non-human animals.

Further Reading

21st Century Principles


The most recent development in animal rights is the emergence of the philosophical and legal principle of personhood. It argues that certain animals, most notably the great apes, demonstrate a sufficient level of “personhood” to justify being deemed deserving of human rights.

The philosophy can be seen as a meeting of two distinct intellectual disciplines: the philosophical study of personhood movement and zoological discoveries. The philosophical study of personhood has its modern roots in the attempts by philosophers to define the term “person” and to identify the features common to all “persons”. The modern debate emerged initially from the philosophical study of abortion, with the debate focusing on if/when a foetus gains personhood status. It has subsequently emerged into a broader study of the nature of personhood.

There is no clear consensus on the definition of “personhood”. Some philosophers are unwilling to define personhood with reference to a human’s sentience, intelligence or rationality, as this may lead to certain humans, including foetuses and the severely developmentally disabled being denied personhood. Supporters of this position include Frances Beckwith, who argued that personhood should not be limited to considering the intellectual skills of a human. Rather, personhood applies to all those “entities” capable of progressing to become a human. In essence, personhood is equated with being human. For some philosophers, this is regarded as an almost genetic argument – personhood belongs to all those who have the genetic make-up of a human.

Other philosophers argue against this position, and argue that not all humans are persons. Only those with set features qualify as persons, as it is those features that truly define the concept of a person. For example, philosopher Thomas White argues a person is any creature that is: (a) alive, (b) aware, (c) capable of feeling positive and negative sensations, (d) capable of feeling emotions, (e) has a sense of self, (f) controls their behaviour (g) recognises others with personhood and (h) has a variety of cognitive abilities.

Finally (and this is not an attempt to explore exhaustively the personhood debate) some philosophers, perhaps best described as legal realists, argue that personhood should be regarded as a legal construct, designed to ensure that those deserving of protection under the law are properly recognised. As such, personhood should extend to those who deserve recognition under the law. Under this principle, these philosophers base their definition of personhood with factors that make a entities deserving of legal protection.

Whilst this philosophical debate was developing, the scientific study of primatology and zoology was also making significant discoveries. These discoveries were capable of demonstrating that an enormous array of non-human animals demonstrated traits that would qualify them for personhood, regardless of the particular definition chosen.

For example, the mapping of the genomes of great apes showed that humans share 98.8% of their DNA with bonobos and chimpanzees. Indeed, there is approximately the same difference between gorillas and chimps as there is between humans and bonobos. If personhood is to be awarded to persons based simply on their genetic makeup, it becomes difficult to justify denying similar status to non-human animals that have almost 99% of our own genetic make-up. Many academics argue that such a distinction is an arbitrary and unjustifiable distinction.

Other studies show personhood could be justified on the basis proposed by philosophers such as Thomas White. Again, studies into primates have revealed that the great apes and other primates have an enormous capacity for cognitive and emotional processing. Perhaps most famously, Koko the gorilla; a western lowland gorilla, has been the subject of linguistic and emotional studies for almost 40 years. Researchers working with Koko claim that she has learned almost 2000 words and can construct complicated sentences, comparable to the sentences used by a young human child. These studies have revealed a great deal of emotional and intellectual awareness. Other studies into an array of animals, including primates and birds, most notably those from the corvidae family, show that many other animals have capabilities that would make them suitable for personhood.

As a result of these zoological developments, there has been a movement amongst the international legal and zoological community to fight to extend personhood to animals. The Great Ape Project (1993) and The Nonhuman Rights Project (2007) both work to extend legal rights to non-human animals, and have prominent supporters, included Richard Dawkins, Jane Goodall and Peter Singer.

There have been significant legal successes as a result of the personhood movement. In 1999, New Zealand extended legal protections to chimpanzees, gorillas, orang-utans and bonobos, forbidding testing and research on them. In 2002, Germany became the first country in the European Union to guarantee rights for animals. In February 2007, the Balearic Islands passed legislation that effectively granted legal rights to all great apes; chimpanzees orang-utans, bonobos and gorillas.

A series of cases have also attempted to extend human rights to primates. In 2000, the High Court of Kerala handed down an opinion that stated: "It is not only our fundamental duty to show compassion to our animal friends, but also to recognize and protect their rights. ... If humans are entitled to fundamental rights, why not animals?"

It is reported that in January 2015, a court in Argentina considered the case of Sandra the orangutan. She had been kept in squalid conditions in Buenos Aires Zoo for 20 years when the Argentina’s Association of Professional Lawyers filed a writ of habeas corpus on Sandra’s behalf. The Argentine Federal Chamber of Criminal Cassation concluded that Sandra was a “nonhuman being” and therefore entitled to basic rights, such as life, freedom and to be free from psychological and physical harm. As a result, she was moved to a rescue and rehabilitation centre.

There have been failures. The courts in several countries have rejected applications to extend human rights to animals. For example, in January 2006 in New York, the New York Supreme Court declined to issues a writ of habeas corpus on behalf of Tommy the Chimpanzee, concluding that he was not entitled to the writ. But the fight hasn’t ended. The Nonhuman Rights Project are currently campaigning for a writ of habeas corpus in for two chimpanzees; Hercules and Leo, who are currently being held in a research centre in Louisiana.

Further Reading


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