Relation to the world· Mind and consciousnessCommon view

Substance dualism

Axis: The enigma of consciousness — Is lived experience something more than the structure and functioning of the brain?

The brain will never fully explain experience, because consciousness is not its product: it is a reality of another nature, the soul, which could in principle exist apart. The spontaneous view of many and of many religions, it is also defended by philosophical arguments: if I can conceive my mind without my body, perhaps the two are not one single thing.

Who holds this position

Movements 1

Platonismexplicit

What thinks cannot be of the same nature as what is thought from without: the soul knows the immaterial , it moves itself and outlasts the body's states, traits no arrangement of matter could produce. Consciousness thus belongs to an order other than the sensible, prior to and independent of it, not to a bodily configuration that would generate it. Platonism thereby refuses in advance any of mind to matter, where the will make the soul a corporeal breath.

Plato, Phaedo; Phaedrus

Philosophers 1

Descartesexplicit

The argument rests on a principle: what I clearly and distinctly conceive as able to exist apart really exists apart, since God could create it so. Now I can conceive my mind, pure thinking thing (res cogitans), with nothing corporeal attributed to it, and body, pure extension (res extensa), with no thought. My essence is therefore to think, and the mind is really distinct from the body, a substance of another nature than the brain. This substance dualism breaks with the Aristotelian soul, form of a body, and at one stroke frees matter for a purely mechanistic physics; yet it bequeaths the problem, which Descartes will struggle to solve, of their union and interaction.

Meditations on First Philosophy, VI

Arguments and objections

ArgumentThe argument from the indivisibility of mind — Whatever occupies space divides; the subject that thinks does not: two things with opposite properties are not one.

Whatever is material is divisible: a body, an organ, a brain can be parted, and each part is still something extended. That is what it means, for a thing, to occupy space.
What thinks is not parted in that way: when I deliberate, I do not find one half of me doubting and another willing, but a single subject that doubts, wills and feels. Removing a part of a thought does not leave a smaller thought, it leaves nothing.
Yet two things that do not share the same properties cannot be one and the same: if one divides and the other does not, then there are two.

Therefore So what thinks in me is not what is extended: mind is a reality of another kind, and its dependence on the body does not prove it to be a part of it: this is the thesis of substance .

ObjectionAttacks the reasoningThe divided-brain objection — The sense of being one may be no more than the effect of an intact brain: severed, it doubles.

The argument rests entirely on one premise: what thinks cannot be parted. If it falls, the distinction between the indivisible mind and the divisible body falls with it.
Yet in epileptic patients the bundle joining the two hemispheres has been severed, producing what is called a split brain. They live normally afterwards; but in certain tests one hand points to what the subject declares not to see, and he at once invents a reason for the gesture. One and the same brain then seems to host two streams of experience that ignore each other.
The sense of being one therefore does not prove one is dealing with a simple substance: it may be the product of successful communication between parts, and it comes apart when that communication is cut.
Long before such operations, mental life showed its seams: what admits of degrees (sleep, drunkenness, dementia), what dissociates, what is built up in stages in a child, resembles an assembly rather than something indivisible, and joins the question of .

Therefore The mind's indivisibility is not a given: it is an appearance produced by an intact brain. The argument's decisive premise falls.

ObjectionAttacks the positionElisabeth of Bohemia's objection — The purer the soul, the less one understands how it could raise an arm: dualism saves the mind at the price of its commerce with the body.

One thing moves another only by touching it, or by acting on it through a force that has a direction and a point of application: this is how we understand any action, from colliding balls to the signal running along a nerve.
But an unextended mind is nowhere, has neither surface nor force: it meets none of the conditions by which we understand one thing to modify another.
One would then have to admit an action of an entirely unprecedented kind, of which nothing can be said except that it occurs. That is not explaining the union of soul and body, it is giving it a name.
And the puzzle is twofold, for the mind would also have to be reached by the body: a blow, a fever, a glass of wine immediately change what I think and what I feel, as if matter had purchase on what is not matter.

Therefore Dualism saves the mind's irreducibility at the price of its commerce with the body: the purer the soul, the less one understands how it could raise an arm.

Foundations and implications

↑ What grounds it

↓ What it implies

↑ What grounds it

Nature of reality

If reality comprises two irreducible substances, extended matter and thought, then my consciousness belongs to the second: it is not the brain but a reality of another nature. Metaphysical dualism directly grounds substance dualism in the philosophy of mind, of which Descartes gives the classic formulation.

↓ What it implies

Moral circle

If only the rational soul confers genuine inwardness, animals, lacking this thinking substance, are nothing but mechanisms without worth of their own. Substance dualism supports moral anthropocentrism: for Descartes, the "animal-machine" does not enter the circle of our direct duties. The link is looser, however, among anthropocentrists who, like Kant, ground dignity in reason rather than in a soul-substance.

Being or having a body

If I am essentially a mind distinct from matter, my body becomes an instrument I use, even a prison I set myself apart from. Substance dualism supports the body-as-instrument conception, from Plato to Descartes, even though the latter eventually insisted on the union of soul and body.

Freedom of the will

If the mind does not belong to the mechanical order of matter, the will escapes the determinism of physical causes and can determine itself. Substance dualism thus supports free will, by removing decision from the chain of natural causes.

After death

If the mind is a substance distinct from the body, its survival becomes conceivable: substance dualism is the metaphysical ground of the immortal soul, from Plato to Descartes.

Nature of the self

If the mind is a substance distinct from the body, the self that says "I" is this thinking thing, identical to itself beneath the flow of experiences. Substance dualism grounds substantialism: personal identity rests on the permanence of the soul, not on memory or narrative. This is Descartes' position.

Problems

Descriptive Thought experiment
What it is like
There is something it is like to be me, and nothing of the sort, presumably, for a stone. But is that "something" one more reality in the world, which physical description lets slip, or only a limit of ours, unable as we are to occupy another's point of view?
a being's point of view
Descriptive Thought experiment
Mary's room
A scientist knows everything physics can say about colour, without ever having seen any: the day she sees red, does she learn something? If she does, lived experience would be one more fact, which objective knowledge did not contain; if not, one must say what she gains while learning nothing.
a lived experience
Descriptive
The knot of mind and body
My decision raises my arm, a glass of wine muddles my thinking. But if the mind is not material, how does it act on muscles; and if the physical order is self-sufficient, does experience change anything at all in what happens?
the reciprocal action of mind and body
Descriptive
Is my mind transparent to me?
I believe I know better than anyone what I think and feel. But the mind may exceed what it perceives of itself: what if introspection told, after the fact, a story about a mental life that largely escapes it?
one's own mental life
Descriptive
Minds other than my own
I never perceive another's experience, only bodies behaving: how do I know there is someone behind them? The only consciousness I have direct testimony of is my own.
access to another's experience
Descriptive
What holds experience together
At every moment I see, hear and think at once, yet all of it comes to me as a single experience. What holds it together? When the bridge between the two hemispheres is severed, one and the same brain seems to host two streams of experience that ignore each other.
the unity of the field of consciousness
Descriptive
The instrument or the source
A glass of wine, a lesion, age: the body alters thinking down to character itself. Does this dependence prove that the mind is bodily through and through, or only that its instrument is damaged, like a musician with a broken violin?
the mind's dependence on the body