What Is the Soul?

Quick Answer

What is the soul? The question is one of the oldest in philosophy, and the word "soul" has carried a range of meanings: the principle of life, the seat of consciousness, the subject of thought and desire, the core of personal identity, and the part of us that might survive death. Plato gave the soul its most influential philosophical definition: an immaterial, immortal substance that is separable from the body and whose liberation is the goal of the philosophical life. Aristotle redefined it: the soul is the form of the body, the principle of organization and activity that makes a living thing what it is — not a separate thing that inhabits the body but the very structure of its functioning. Augustine inherited both traditions and transformed them: the soul is created by God, immaterial, and immortal, and the person is the union of soul and body, to be completed only at the resurrection. Modern philosophy of mind has asked whether the concept of the soul survives the rise of neuroscience: if mind and consciousness are functions of the brain, then "soul" either names a function, a social construction, or an illusion. The question "what is the soul" is therefore inseparable from the question "what is a person." This page is a philosophical and educational discussion; it is not medical or religious advice.

Historical Background

The Greek concept of the soul (psyche) originally meant the principle of life: whatever makes a living thing alive, from plants to gods. Plato transformed it: the psyche becomes the seat of reason and the immortal part of the person. In the Phaedo, Socrates argues that the soul is akin to the Forms — eternal, simple, and unchanging — and that death is the separation of soul from body, which the philosopher welcomes as release. In the Republic, Plato analyzes the soul into reason, spirit, and appetite, arguing that justice in the soul mirrors justice in the city. Aristotle rejected the separation of soul and body. In the De Anima, he defines the soul as "the first actuality of a natural body that has life in potentiality" — the form or organization of the living body, in the way that the shape and arrangement of an axe makes it an axe. The soul, for Aristotle, cannot exist without the body, except for the problematic case of the active intellect. The Hellenistic schools were materialist about the soul: Epicurus held it is composed of fine atoms, and the Stoics that it is a kind of fiery breath. Augustine, in the late Roman Empire, synthesized Plato and Christianity: the soul is a created, immaterial substance, the image of God, which survives death and awaits reunion with the body. The medieval synthesis, completed by Thomas Aquinas, gave the soul a precise definition: the substantial form of the body, immortal, and created directly by God for each person. Modern philosophy — from Descartes's dualism of mind and body to contemporary physicalism — has continued to ask what, if anything, the soul is, and whether the concept can survive the scientific study of the mind.

Key Concepts

Plato: the soul as immortal substance. For Plato, the soul is a simple, immaterial substance that pre-exists the body, is imprisoned in it, and survives its death. The arguments of the Phaedo — from recollection, from opposites, from simplicity — support the soul's immortality. The philosophical life is a practice of dying: the purification of the soul from bodily attachment, so that at death the soul is fit to return to the intelligible realm. Plato's conception grounds the hope of an afterlife and the ethics of care for the soul, but it raises the question of how an immaterial soul could be united with a material body.

Aristotle: the soul as form of the body. Aristotle's definition solves the union problem by denying the separation: the soul is not a thing in the body but the body's organized way of being alive. Just as the shape of a statue is not a separate substance, the soul is not a separate substance but the form that organizes matter into a living being. The soul has parts corresponding to life's capacities — nutrition, perception, desire, locomotion, thought — and the higher capacities presuppose the lower. On this view, there is no question of the soul's surviving the body, except for the contested case of the active intellect, which Aristotle describes as separable and immortal in a passage that has puzzled commentators for two thousand years.

Augustine: the soul in Christian theology. Augustine held that the soul is created by God, immaterial, immortal, and the seat of the image of God in the human person. Death is the separation of soul from body — a consequence of sin — and the soul's fate after death is the beginning of eternal reward or punishment. But Augustine insisted that the person is not complete without the body: the full human being is soul and body together, and the resurrection reunites them. The Augustinian soul is both Platonic (immaterial, immortal, separable) and Aristotelian (the form of the body, completing the person). The synthesis is powerful but inherits the tensions of both traditions.

The modern question. Modern philosophy of mind asks whether "soul" names anything over and above the mind. Descartes identified the soul with the mind: a thinking substance distinct from extended matter. Physicalists deny that there is any immaterial substance; the mind is the brain, or a function of the brain. Eliminativists go further, suggesting that the concepts of mind and soul may be replaced by the vocabulary of neuroscience. Between these poles, philosophers ask whether the concept of the soul survives as a way of speaking about the person, the self, or the unity of consciousness — and whether anything is lost when we stop using it.

Key Arguments

The argument from simplicity. Plato's affinity argument: the soul is akin to the Forms — simple, incomposite, unchanging — and what is simple cannot be destroyed, since destruction requires the dissolution of parts. The argument is elegant but vulnerable: even if the soul were simple, the premise that what is simple is indestructible is not obviously true, and the premise that the soul is simple is contested by Plato's own tripartite analysis in the Republic.

The argument from function. Aristotle's argument that the soul is the form of the body: since the soul is the actuality of a living body, and since forms do not exist apart from the matter they inform (except in the problematic case of the intellect), the soul cannot survive the body. The argument grounds the unity of the person and the dependence of mental life on the body — a conclusion that resonates with modern neuroscience.

The argument from consciousness. The modern defense of something like the soul: consciousness is the one thing we know directly, and its existence is not explained by the physical description of the brain. The hard problem of consciousness — why there is subjective experience at all — keeps alive the possibility that mind is not exhausted by matter. This argument does not prove the soul's immortality, but it blocks the simple dismissal of the concept.

The argument from personhood. The theological and existential argument: the soul names what is irreplaceable in a person — the subject of dignity, responsibility, and love. Even if the metaphysics of the soul is uncertain, the concept organizes our sense of what matters about human beings. This argument concerns the meaning of the concept rather than its referent.

Contemporary Relevance

The concept of the soul remains practically important even in a scientific age. It organizes religious belief and practice, including funeral rites, prayers for the dead, and hope for reunion. It underwrites the dignity of the human person in bioethics: debates about abortion, euthanasia, and the definition of death often turn on when the soul — or its secular equivalent, the person — begins and ends. In the clinic, the question of whether consciousness survives death is alive in the study of near-death experiences and in the definition of brain death. In philosophy, the concept of the soul has been largely replaced by the concepts of mind, self, and person, but the questions the concept once answered — What is a person? What survives death? What is irreplaceable about a human life? — remain central. Philosophy's contribution is to keep the question honest: to distinguish the empirical claims from the conceptual ones, and to ask what is at stake in saying that we have, or are, souls. This page is educational and philosophical; it is not medical or religious advice.

Related Topics

• What Is the Self? — the modern concept that inherits the soul's role.
• Is There Life After Death? — whether anything survives bodily death.
• What Is the Afterlife? — the fate of the soul after death across traditions.
• What Happens to Consciousness When We Die? — the fate of conscious experience at death.
• What Is the Death of the Self? — whether the self survives, on Parfit's account.

Sources

1. Stanford Encyclopedia of Philosophy, Ancient Theories of the Soul.
2. Stanford Encyclopedia of Philosophy, Dualism.
3. Stanford Encyclopedia of Philosophy, Plato.
4. Stanford Encyclopedia of Philosophy, Aristotle.
5. Stanford Encyclopedia of Philosophy, Augustine.