The soul is most commonly understood as the non-physical, essential part of a person that persists beyond the death of the body. Religions differ sharply on its nature; philosophers have proposed radically different accounts of how it relates to the body; and the scientific consensus holds that mental life depends on the brain, leaving the soul’s independent existence unconfirmed by any reproducible evidence.
| Tradition or school | What the soul is | What happens to it |
|---|---|---|
| Christianity | Immaterial, individual self created by God | Survives death; faces judgement |
| Hinduism (atman) | Universal, eternal core of the personality | Transmigrates or attains release |
| Buddhism (anatta) | No permanent soul exists | A changing stream of factors disperses |
| Plato | Immaterial substance, separable from the body | Continues after death; argued for rationally |
| Aristotle | The form or organisation of the living body | Does not survive the body’s dissolution |
| Descartes | Thinking substance, distinct from extended matter | Distinct from the body; can in principle outlast it |
| Modern materialism | Mental life is a function of the brain | Ceases when the brain ceases |
Religious Accounts of the Soul
Christianity
Within Christianity the soul is generally understood as an immaterial, individual principle that God creates and that gives each person their moral identity. The body and soul are seen as genuinely distinct: the body is mortal while the soul can persist beyond physical death and face divine judgement. Different Christian traditions have debated whether the soul sleeps between death and resurrection or is immediately conscious in another realm, but the broad consensus across Catholic, Orthodox and most Protestant theology is that the soul is real, individual and survives bodily death. Questions about what that survival looks like connect directly to Christian understandings of heaven and afterlife belief.
Hinduism and the Atman
Hinduism offers one of the most developed accounts of the soul found in any religious tradition. The atman is the universal self, understood as the eternal core of the personality. It is not simply an individual possession in the way a Christian soul might be; in many strands of Hindu philosophy the atman is ultimately identical with Brahman, the universal ground of being. After death the atman transmigrates into another body, the particular body being determined by karma accumulated across lifetimes. The goal of spiritual practice, in many Hindu schools, is moksha: the liberation of the atman from the cycle of rebirth, either by reunion with Brahman or by the soul’s dwelling in permanent relationship with a personal God.
Buddhism and the Doctrine of Anatta
Buddhism takes a position that is striking compared with almost every other major tradition: it denies that there is a permanent, underlying substance that can be called the soul. This doctrine is known as anatta, often translated as “no-self.” A person, on the Buddhist account, is compounded of five changing factors, sometimes called aggregates: form, sensation, perception, mental formations and consciousness. None of these factors is permanent, and no additional entity underlies them. The sense of being a continuous, unified self is, on this view, a kind of construction rather than a discovery of something real.
This does not mean Buddhism denies continuity altogether. The stream of causes and conditions that constitutes a person does continue across lifetimes in Buddhist thought, but what continues is a process, not a substance. The goal, as in Hinduism, is liberation from the cycle of rebirth, though the account of what is liberated differs sharply between the two traditions.
Classical Philosophical Accounts
Plato: The Soul as Separable Substance
Among the philosophers of ancient Greece, Plato developed the most systematic and influential account of the soul as an entity separable from the body. His dialogue the Phaedo sets out several arguments for the conclusion that the soul will continue to exist after death. The dialogue presents Socrates on the day of his execution, reasoning with friends about why death need not be feared.
One line of argument in the Phaedo runs from the nature of knowledge: Plato holds that genuine knowledge is knowledge of eternal, unchanging forms, and that the soul must therefore be akin to those forms, itself unchanging and therefore not subject to destruction. Another argument appeals to opposites: life and death succeed one another as opposites do, so just as sleeping gives way to waking, death gives way to life again. A further argument holds that the soul, being simple and uncomposed, cannot be broken apart the way composite things can.
These arguments have been debated by philosophers for many centuries. Critics have pointed out that simplicity does not guarantee indestructibility, and that the analogy between opposites proves less than Plato intends. Nonetheless, the Phaedo set the terms of discussion that Western philosophy would return to repeatedly, and Plato’s basic picture of the soul as a non-physical substance temporarily housed in a body remained enormously influential throughout the medieval period and beyond.
Aristotle: The Soul as Form of the Body
Aristotle rejected his teacher’s account of the soul as a separable substance. Aristotle identified the soul of a living creature with its form: the organisation of the living body. On this view the soul is not a separate thing housed inside the body; it is the body’s being alive and functional. Just as the ability to cut is not a separate entity housed inside an axe but simply what the axe is when it is working, the soul is what the body is when it is living.
This account has several consequences. First, it makes the soul deeply dependent on the body: damage the body severely enough, and the soul is gone, because the soul just is the body’s organisation. Second, it allows Aristotle to explain a wide range of biological and psychological phenomena in a unified way, since all living things have souls of one kind or another. Plants have nutritive souls, animals have nutritive and sensitive souls, and humans add a rational soul on top. Third, it makes personal survival of death much harder to maintain, at least on the same terms as Plato’s account, since the destruction of the body is the destruction of the soul’s basis.
Aristotle does gesture towards the possibility that the intellect, or some part of it, might be separable, but he never develops this point consistently. His account, known as hylomorphism from the Greek words for matter and form, influenced medieval Christian and Islamic philosophy deeply, particularly through attempts to reconcile Aristotelian form-theory with Christian doctrines of personal immortality.
Descartes: Dualism and Two Substances
René Descartes revived a sharp separation between mind and body in early modern philosophy. Descartes argued that mind and body are distinct substances: the mind is characterised by thought and the body by extension, meaning occupation of space. Nothing that thinks need occupy space, and nothing that occupies space need think. On this view the soul, identified with the mind, is a genuinely different kind of thing from the material body, and the two interact with one another during a person’s lifetime.
Descartes’ dualism set a new agenda for philosophy of mind. It made certain questions very sharp: if mind and body are genuinely different substances, how do they interact? This is the classic mind-body problem. Subsequent philosophers proposed various answers, including parallelism, occasionalism and idealism. None of these alternatives won consensus, and the difficulty of explaining mind-body interaction has remained a central challenge for anyone who accepts substance dualism.
The Scientific and Modern Philosophical View
The growth of neuroscience over the past two centuries has shifted the terms of the debate substantially. The working hypothesis of modern brain science is that mental processes, including consciousness, memory, personality and emotion, are produced by physical processes in the brain. Evidence for this comes from several directions. Damage to specific brain regions reliably alters or destroys specific mental capacities. Drugs and anaesthetics that act on the brain alter or extinguish conscious experience. The gradual loss of personality and memory in conditions that destroy brain tissue is consistent with mental life depending on brain structure rather than on a separate soul.
None of this strictly proves that there is no soul in the religious sense, since a philosophical dualist can always argue that the soul uses the brain as its instrument and is impaired when the instrument is damaged. However, it does shift the burden of argument: the simpler explanation of the evidence is that mental life is what a functioning brain does, not that a separate substance is operating through the brain.
Among professional philosophers, the 2020 PhilPapers survey found that 51% favoured materialism about the mind, the view that mental phenomena are ultimately physical, while 22% favoured dualism. The majority position among those who study these questions most carefully is therefore that the mind does not require a non-physical soul to explain it, though a substantial minority continues to defend some form of dualism.
These debates about the nature of the mind connect to broader questions about whether there is good reason to believe in a God who could create and sustain souls, questions that the article on whether God is real examines in more detail.
Claims to Have Detected the Soul: The 21 Grams Experiment
The most widely known attempt to detect the soul by physical measurement was carried out in 1907 by the physician Duncan MacDougall. MacDougall placed 6 dying patients on a specially constructed balance sensitive enough to detect small changes in weight, and claimed to observe a loss of about 21 grams at the moment of death. He interpreted this as the departure of the soul from the body. The figure became famous and has persisted in popular culture ever since, the idea being that the soul has a measurable, if tiny, mass.
MacDougall also ran the same experiment with 15 dying dogs and found no weight loss. He took this as confirmation of his human results, since Christian theology holds that animals lack immortal souls.
The experiment has not been confirmed by any subsequent researcher. The problems with MacDougall’s work are substantial. Only 6 patients were tested, and the results across those 6 were not consistent: a weight loss was clearly recorded in only one case. The timing of the supposed weight loss varied across cases, and some apparent changes could be explained by ordinary physical processes such as the cessation of moisture loss through breathing or other bodily functions. No controlled replication has produced the same result, and the scientific community does not regard MacDougall’s claim as valid evidence for the soul’s existence.
The persistence of the 21 grams figure in popular culture illustrates how an isolated, unreplicated claim can outlast the scrutiny that dismantled it. The soul’s existence cannot be confirmed or refuted by weighing the body at death; a non-physical substance, by definition, would have no mass to measure, so this kind of test cannot settle the question even in principle.
Related claims about experiences at the border of death, which some people take as evidence for the soul’s independence from the brain, are examined in the article on near-death experiences and the soul.
Where the Accounts Agree and Where They Diverge
Across these very different traditions, a few common themes recur. Almost all soul-theories are motivated by the intuition that a person is more than a lump of matter, that there is something it is like to be a person that cannot be fully captured by a description of physical processes. They are also motivated, in religious contexts, by the need to give an account of personal identity over time, moral responsibility and the possibility of a meaningful existence beyond death.
The accounts diverge most sharply on three questions. First, is the soul a substance in its own right, as Plato and Descartes argued, or is it inseparable from the body, as Aristotle held and as modern materialism implies? Second, is the soul individual, as Christianity maintains, or is individuality itself ultimately an illusion, as some strands of Hinduism and Buddhism suggest? Third, is there any reproducible evidence that the soul can exist independently of a functioning body?
On that third question, the honest answer at present is that no reproducible evidence exists. That does not settle the philosophical debate, since absence of evidence is not always evidence of absence, and many philosophers argue that consciousness raises genuine puzzles that materialism has not yet fully resolved. It does mean, however, that confidence in a soul’s independent existence rests on religious conviction, philosophical argument or personal experience rather than on confirmed empirical findings.
Frequently Asked Questions
Does Buddhism believe in a soul?
No. Buddhism’s doctrine of anatta explicitly denies that there is a permanent, underlying substance that can be called the soul. A person is understood as a compound of five changing factors, none of which is a fixed self. What continues across lifetimes is a stream of causes and conditions, not a substance.
What did Plato argue about the soul in the Phaedo?
In the Phaedo, Plato presents several arguments that the soul will continue to exist after death. The arguments draw on the soul’s kinship with eternal forms, the succession of opposites, and the soul’s supposed simplicity and indestructibility. These arguments have been extensively criticised, but they set the terms of Western philosophical debate about immortality for many centuries and remain widely discussed today.
How did Aristotle’s view of the soul differ from Plato’s?
Aristotle identified the soul with the form or organisation of the living body, not with a separate substance housed inside it. This makes the soul deeply dependent on the body: the soul is what the body is when it is alive and functioning. Personal survival of death is very difficult to maintain on Aristotle’s account, unlike on Plato’s, since destroying the body destroys the basis of the soul.
What was the 21 grams experiment, and is it reliable?
In 1907 the physician Duncan MacDougall weighed 6 dying patients and claimed a loss of about 21 grams at death, which he interpreted as the soul departing the body. He found no such loss in 15 dying dogs. The experiment has never been confirmed by subsequent researchers: the results across MacDougall’s own patients were inconsistent, and the scientific community does not regard the experiment as valid evidence for the soul’s existence.
What do philosophers today think about the soul and the mind?
The 2020 PhilPapers survey found that 51% of philosophers favoured materialism about the mind and 22% favoured dualism. The majority view among professional philosophers is therefore that mental life does not require a non-physical soul to explain it, though a substantial minority defends some form of dualism.
What is the difference between the Hindu atman and the Christian soul?
The Christian soul is typically understood as an individual, created by God and remaining individual through eternity. The Hindu atman is the universal self, and in many strands of Hindu philosophy it is ultimately identical with Brahman, the universal ground of being, so individuality is finally transcended rather than preserved. Both traditions agree that this essential self survives death; they differ on what that survival ultimately means.
Summary
The soul is defined differently depending on the tradition or framework being applied. In Christianity it is an individual, immaterial self that survives death and faces judgement. In Hinduism the atman is the eternal core of the personality, ultimately one with the universal ground of being. Buddhism denies that any permanent self exists, understanding persons as compounds of five changing factors. Philosophically, Plato argued in the Phaedo that the soul is a separable substance that continues after death; Aristotle identified the soul with the form of the living body, making survival much harder to defend; and Descartes argued that mind and body are genuinely distinct substances, reviving dualism for the modern era. The modern scientific view holds that mental life depends on the brain, a position supported by the majority of professional philosophers in the 2020 PhilPapers survey, where 51% favoured materialism and 22% dualism. The most famous attempt to detect the soul physically, Duncan MacDougall’s 1907 experiment claiming a loss of about 21 grams at death, has never been confirmed and is not considered valid evidence by the scientific community. The question of what the soul is, and whether it exists independently of the body at all, remains one of the most contested in both philosophy and religion.
Sources
- Stanford Encyclopedia of Philosophy, "Dualism" (first published 2003, revised 2025). plato.stanford.edu.
- Joe Schwarcz, "The Real Story Behind 21 Grams", McGill Office for Science and Society (19 June 2019). mcgill.ca.