Sentience is the ability to feel, perceive or be conscious, or to have subjective experiences. Eighteenth century philosophers used the concept to distinguish the ability to think ("reason") from the ability to feel ("sentience"). In modern western philosophy, sentience is the ability to have sensations or experiences (described by some thinkers as "qualia"). For Eastern philosophy, sentience is a metaphysical quality of all things that requires respect and care. The concept is central to the philosophy of animal rights, because sentience is necessary for the ability to suffer, which entails certain rights. In science fiction, non-human characters described as "sentient" typically have similar abilities, qualities and rights as human beings.
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In the philosophy of consciousness, "sentience" can refer to the ability of any entity to have subjective perceptual experiences, or "qualia".[1] This is distinct from other aspects of the mind and consciousness, such as creativity, intelligence, sapience, self-awareness, and intentionality (the ability to have thoughts that mean something or are "about" something). Sentience is a minimalistic way of defining "consciousness", which is otherwise commonly used to collectively describe sentience plus other characteristics of the mind.
Some philosophers, notably Colin McGinn, believe that sentience will never be understood, a position known as "new mysterianism". They do not deny that most other aspects of consciousness are subject to scientific investigation but they argue that subjective experiences will never be explained; i.e., sentience is the only aspect of consciousness that can't be explained. Other philosophers (such as Daniel Dennett) disagree, arguing that all aspects of consciousness will eventually yield to scientific investigation.
Eastern religions including Hinduism, Buddhism, Sikhism, and Jainism recognize nonhumans as sentient beings. In Jainism and Hinduism, this is closely related to the concept of ahimsa, nonviolence toward other beings. In Jainism, all matter is endowed with sentience; there are five degrees of sentience, from one to five. Water, for example, is a sentient being of the first order, as it is considered to possess only one sense, that of touch. Man is considered to be a sentient being of the fifth order. According to Buddhism, sentient beings made of pure consciousness are possible. In Mahayana Buddhism, which includes Zen and Tibetan Buddhism, the concept is related to the Bodhisattva, an enlightened being devoted to the liberation of others. The first vow of a Bodhisattva states: "Sentient beings are numberless; I vow to free them."
Sentience in Buddhism is the state of having senses (sat + ta in Pali, or sat + tva in Sanskrit). In Buddhism, the senses are six in number, the sixth being the subjective experience of the mind. Sentience is simply awareness prior to the arising of Skandha. Thus, an animal qualifies as a sentient being.
In the philosophy of animal rights, sentience implies the ability to experience pleasure and pain. Animal-rights advocates typically argue that any sentient being is entitled at a minimum to the right not to be subjected to unnecessary suffering, though they may differ on what other rights (e.g., the right to life) may be entailed by simple sentience.
The 18th-century philosopher Jeremy Bentham compiled Enlightenment beliefs in Introduction to the Principles of Morals and Legislation (second edition, 1823, chapter 17, footnote), and he included his own reasoning in a comparison between slavery and sadism toward animals:
The French have already discovered that the blackness of the skin is no reason why a human being should be abandoned without redress to the caprice of a tormentor [see Louis XIV's Code Noir]... What else is it that should trace the insuperable line? Is it the faculty of reason, or, perhaps, the faculty of discourse? But a full-grown horse or dog is beyond comparison a more rational, as well as a more conversable animal, than an infant of a day, or a week, or even a month, old. But suppose the case were otherwise, what would it avail? The question is not Can they reason? nor, Can they talk? but, Can they suffer?
In the 20th century, Princeton University professor Peter Singer argued that Bentham's conclusion is often dismissed by an appeal to a distinction that condemns human suffering but allows non-human suffering, typically "appeals" that are logical fallacies (unless the distinction is factual). Because many of the suggested distinguishing features of humanity—extreme intelligence; highly complex language; etc.—are not present in marginal cases such as young or mentally disabled humans, it appears that the only distinction is a prejudice based on species alone, which animal-rights supporters call speciesism—that is, differentiating humans from other animals purely on the grounds that they are human.
Gary Francione also bases his abolitionist theory of animal rights, which differs significantly from Singer's, on sentience. He asserts that "all sentient beings, humans or nonhuman, have one right: the basic right not to be treated as the property of others."[2]
Andrew Linzey, founder of the Oxford Centre for Animal Ethics in England, is known as a foremost international advocate for recognizing animals as sentient beings in Biblically-based faith traditions. The Interfaith Association of Animal Chaplains encourages animal ministry groups to adopt a policy of recognizing and valuing sentient beings.
In 1997 the concept of animal sentience was written into the basic law of the European Union. The legally-binding Protocol annexed to the Treaty of Amsterdam recognizes that animals are "sentient beings", and requires the EU and its Member States to "pay full regard to the welfare requirements of animals".
The laws of several states include certain invertebrates such as cephalopods (octopuses, squids) and decapod crustaceans (lobsters, crabs) in the scope of animal protection laws, implying that these animals are also judged to be capable of experiencing pain and suffering.[3]
David Pearce is a British philosopher of the negative utilitarian school of ethics. He is most famous for his advocation of the idea that there exists a strong ethical imperative for humans to work towards the abolition of suffering in all sentient beings.
Although the term "sentience" is avoided by major artificial intelligence textbooks and researchers,[4] it is sometimes used in popular accounts of AI to describe "human level or higher intelligence" (or strong AI). This is closely related to the use of the term in science fiction.
In science fiction, an alien, android, robot, hologram, or computer who is described as sentient is usually treated as a fully human character, with similar rights, qualities, and capabilities as any other character. Foremost among these properties is human level intelligence (see above), but sentient characters also typically display desire, will, consciousness, ethics, personality, insight, and many other human qualities. Sentience is being used in this context to describe an essential human property that brings all these other qualities with it. The words "sapience", "self-awareness", and "consciousness" are used in similar ways in science fiction.
Some science fiction plot lines explore ethical concerns analogous to the concerns of advocates of animal rights. In an episode of Star Trek: The Next Generation, "The Measure of a Man", Data, a sentient android, takes legal action to prove that he has the same rights as a human being. In the Star Trek: Voyager episode "Author, Author" the Doctor, a holographic program by nature, fights for his rights as a sentient lifeform. The film A.I. Artificial Intelligence considers a machine in the form of a small boy which has been given the ability to feel human emotions, including the capacity to suffer. In these examples, sentience plays the same role as it does in the philosophy of animal rights.
In many science fiction works sentience is often used as a synonym for sapience meaning "human-level or higher intelligence". But others make a distinction; for example, in David Brin's Uplift stories, the Tandu are undoubtedly sapient (both technologically skilled and cunning) but only marginally sentient, since they regard other races and sometimes other Tandu mainly as potential prey.
The sentience quotient concept was introduced by Robert A. Freitas Jr. in the late 1970s.[5] It defines sentience as the relationship between the information processing rate of each individual processing unit (neuron), the weight/size of a single unit, and the total number of processing units (expressed as mass). It was proposed as a measure for the sentience of all beings living and computer from a single neuron up to a hypothetical being at the theoretical computational limit of the entire universe. On a logarithmic scale it runs from −70 up to +50.