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8 Res Cogitans and Dualism. The immateriality of the soul. Doubt I can doubt whether I have a body, but I cannot doubt that I am or exist. This argument, though, is invalid (see Arnauld’s objection CSM II : 139).

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the immateriality of the soul
The immateriality of the soul
  • Doubt

I can doubt whether I have a body, but I cannot doubt that I am or exist.

This argument, though, is invalid (see Arnauld’s objection CSM II: 139).

From the fact that I doubt that something possesses a given property it doesn’t follow that this very thing lacks it.

The method of doubt concerns one’s subjective perception and this does not prevent physical properties to be essential parts of a thing.

Thus from the fact that I can doubt about me having a body and that I cannot doubt that I am thinking it does not follow that the soul is immaterial.

From “I doubt p & I cannot doubt q” it doesn’t follow that q is not p.

E.g.: From “I doubt that 2+2=4 & I cannot doubt that 3+1=4” it doesn’t follow that 2+2 is not 3+1.

I said in one place that while the soul is in doubt about the existence of all material things, it knows itself preacise tantum—‘in the strict sense only’—as an immaterial substance … I did not at all mean an entire exclusion or negation, but only an abstraction from material things; for I said that in spite of this we are not sure that there is nothing corporeal in the soul, even though we do not recognize anything corporeal in it. (Appendix to Fifth Objections and Replies; CSM II: 276)
  • Thus, the Cartesian doubt cannot constitute a proof of the immateriality of the soul.
the argument from clear and distinct perceptions
The argument from clear and distinct perceptions
  • The arguments which should prove the immateriality of the soul is known as the “Argument for Clear and Distinct Perceptions”.

I can clearly and distinctly perceive the mind apart from body (see fifth meditation).

Arnauld suggested that this argument is similar to the doubt argument (see CSM II: 142).

Arnauld’s argument

One can clearly and distinctly perceive that a triangle has a right angle and yet not clearly and distinctly perceive that it has the Pythagorean property. But even God could not create a right-angled triangle which lacks it.

Descartes’ reply consists in arguing that neither the triangle nor its property can be seen as a complete thing, while the mind and the body must.

A complete thing is a substance that can exist on its own.

Since in my thinking I can conceive the mind/soul to subsist independently of physical properties it is perfectly conceivable that God created my thinking substance without creating the physical ones.

Hence the physical attributes do not belong to the essence of the soul/mind.

  • The concept of mind is complete insofar as one is aware of one’s thinking. And this is sufficient for one to exist with this attribute and this alone. Thinking is the only necessary property of the mind.
the divisibility argument
The Divisibility Argument
  • The mind and body are mutually exclusive. Being extended the body can be divided while the mind is indivisible.

There is a great difference between the mind and the body inasmuch as the body is by its very nature always divisible while the mind is utterly indivisible. For when I consider the mind, or myself in so far as I am merely a thinking thing, I am unable to distinguish any part within myself; I understand myself to be something quite single and complete. Although the whole mind seems to be united to the whole body I recognise that if a foot or an arm or any other part of the body is cut off nothing has thereby been taken away from the mind. (Sixth Meditation;CMS II: 59)

But, what if we take away the brain?

Descartes circumvents this problem in concentrating on pure thought (he recognises that some mental activity such as imagination and sense-perception depends on the brain), e.g. thoughts of abstract objects.

Even if the body is destroyed, the mind or soul would not be harmed: it would merely leave the body. The soul/mind is immortal.

This doctrine, though, has already been established a priori: it does not rest on the divisibility argument.

[T]his power of imagination which is in me, differing as it does from the power of understanding, is not a necessary constituent of my own essence, that is, of the essence of my mind. For if I lacked it, I should undoubtedly remain the same individual as I now am; from which it seems to follow that it depends on something distinct from myself. … the difference between this mode of thinking and pure understanding may simply be this: when the mind understands, it in some way turns towards itself and inspects one of the ideas which are within it; but when it imagines, it turns toward the body and looks at something in the body which conforms to an idea understood by the mind or perceived by the senses. (Sixth Meditation; CSM II: 51)
the immortality of the soul
The immortality of the soul
  • Main Argument

Phase one

Prem. 1: If I can clearly and distinctly understand A apart from B and B apart from A, then God could have created one without the other, and A cannot depend on B for its existence, or B on A.

Prem. 2: I can clearly and distinctly understand myself as a thinking thing apart from body, and a body as an extended thing apart from thought.

PreliminaryConclusion: God could have created my mind in such a way that it does not depend on any body.

Phase two

Prem. 3: God could have created my mind in such a way that it does not depend on any body.

Prem. 4: If A could have been created to be independent of B, A can exist when B no longer exists.

Prem. 5: When I am dead, my body (as such) will no longer exist.

Conclusion: I can exist when my body is dead.

  • This does not prove, though, that the Soul survives after the death. It merely proves that it cansurvive it.

(Cf. Dan Scotus) Some predicates can be conceived apart from one another and, yet, they cannot exist apart from one another:

E.g.: divine justice and divine mercy; it is impossible for God to be just and not merciful as it is impossible for Him to be merciful without also being just.

  • Reply

For it to be the case that we can understand two things distinctly and separately, they must really be entities in their own right.


The ability to employ imagination suggests the presence of the body. If there can be thought without imagination, as Descartes suggests, there can be thought without a body.

Imagination, like perception, is not essential to a subject. Thus, if the souls is immortal it does not involve imagination and perception; it merely requires intellectual understanding.

the mind body divide
The Mind-Body divide
  • Descartes’ Aim

To prove that the mind and the body are

1. real subjects

2. numerically distinct entities

3. can exist without the other

  • Leibniz’s Law and the Identity of Indiscernibles

Leibniz’s law

a = b  (F) (Fa  Fb)

If a and b are identical then each property of a must also be a property of b and vice versa.

Identity of indiscernibles

(F) (Fa  Fb)  a = b

This is the converse of Leibniz’s law and states that if every property of a is also a property of b and vice versa (i.e. there is no discernible difference between them), then a and b are identical.

If a and b have all properties in common, then a and b are identical.


If MIND and BODY have all properties in common, then MIND = BODY

If MIND and BODY differ in some property, then MINDBODY

mind vs body an epistemological distinction
Mind vs. Body: an Epistemological Distinction
  • The mind (x) and the body (y) are distinct =df.

x and y are distinct insofar as x and/or y can be conceived/understood without each other.

[F]or establishing a real distinction it is sufficient that two things can be understood as ‘complete’ and that each one can be understood apart from the other. (Reply to Arnauld; Fourth Set of Replies; CSM II: 156)

Criterion for Distinctness: Clear and Distinct Ideas

Descartes’ criterion of distinctiveness is epistemological.

Yet, since clear and distinct ideas must reflect the true nature of things, distinct ideas reflect distinct substances.

  • Main question

How can ideas be distinct and thus represent different substances?


Descartes draws a comparison between mental intuition (perception) and seeing with the eyes

Indeed there are very many people who in their entire lives never perceive anything with sufficient accuracy to enable them to make a judgement about it with certainty. A perception which can serve as the basis for a certain and indubitable judgement needs to be not merely clear but also distinct. I call a perception ‘clear’ when it is present and accessible to the attentivemind—just as we say that we see something clearly when it is present to the eye’s gaze and stimulate it with sufficient degree of strength and accessibility. I call a perception ‘distinct’ if, as well as being clear, it is so sharply separated from all other perceptions that it contains within itself only what is clear. (Principles of Philosophy 45; CSM I: 207-8)

Direct Mental Apprehension

Descartes’ account of knowledge is thus based on direct mental apprehension.

Mental intuition goes proxy for mental acquaintance/grasping.

In discussing the “action of the intellect by mean of which we are able to arrive to the knowledge of things with no fear of mistake” (Rules for the Direction of the Mind; CSM I: 14), Descartes recognizes two intellectual actions: intuition and deduction.


By ‘intuition’ I do not mean the fluctuating testimony of the senses or the deceptive judgement of the imagination as it botches things together, but the conception of a clear and attentive mind, which is so easy and distinct that there can be no room for doubt about what we are understanding. Alternatively, and this comes to the same thing, intuition is the indubitable conception of a clear and attentive mind which proceeds solely from the light of reason. … Thus everyone can mentally intuit that he exists, that he is thinking, that a triangle is bounded by just three lines, and a sphere by a single surface, and the like. (Rules for the Direction of the Mind; CSM I: 14)

Necessary/Eternal Truth: Depend on God’s Will

They have been created by God and God makes us to recognize them (following Descartes’ method of doubt). God could have created other necessary truths; even the more basic laws of logic could have been different if God wished so.

All eternal/necessary truth depend on God’s will.

[S]ince every basis of truth and goodness depends on his omnipotence, I would not dare to say that God cannot make a mountain without a valley, or bring it about that 1 and 2 are not 3. I merely say that he has given me such a mind that I cannot conceive a mountain without a valley, or sum of 1 and 2 which is not 3; such things involve a contradiction in my conception. (Letter to Arnauld, 29 July 1648; CSMK III: 358-9)
arnauld s challenge
Arnauld’s Challenge
  • Arnauld objects that one cannot go from the subjective fact to an objective fact.

That is, one cannot infer from his subjective state of certainty or uncertainty concerning a given fact, to the objective certainty or uncertainty concerning the fact itself.

Thus once cannot, pace Descartes, infer from the fact that one is certain about the distinction between one’s mind and body, to the fact that the mind and the body are in fact/in reality distinct.

How does it follow, from the fact that he is aware of nothing else belonging to his essence, that nothing else does in fact belong to it? I must confess that I am somewhat slow, but I have been unable to find anywhere in the Second Meditation an answer to this question. (Arnauld; Fourth Set of Objections; CSM II: 140)
  • Arnauld’s argument

It is not possible for (triangle) T to exist without P (the square of the hypotenuse is equal the square of the two sides)

[E]ven if I deny that the square on the hypotenuse is equal to the square on the other two sides, I still remain sure that the triangle is right-angled, and my mind retains the clear and distinct knowledge that one of its angles is a right-angle. And given that it is so not even God could bring it about that the triangle is not right-angled. … But how is my perception of the nature of my mind any clearer than his perception of the nature of the triangle? … Although the man in the example clearly and distinctly knows that the triangle is right angled, he is wrong in thinking that the aforesaid relationship between the squares on the sides does not belong to the nature of the triangle. Similarly, although I clearly and distinctly know my nature to be something that thinks, may I, too, not perhaps be wrong in thinking that nothing else belongs to my nature apart from the fact that I am a thinking thing?Perhaps the fact that I am an extended thing may also belong to my nature. (Arnauld; Fourth Set of Objections; CSM II: 142-3)
Arnauld objects to the following

What we seem to conceive of x, we really conceive of x

  • Arnauld denies Descartes’ epistemic transparency.

Arnauld’s argument rests on the fact that possibility precedes conceivability.

Thus Arnauld seems to deny this, Cartesian, form of argument:

If one can conceive of x that it is F and of y that it is not F, then x  y.

Descartes’ way out of this problem is to propose a reliable, transparent, notion of conceivability. His notion of ideas should supply what we need:

If one entertains an idea of x being F and an idea of y being F-less, then x  y

  • From the distinctness of ideas one can derive the distinctness of the entities the ideas are about.

But ideas must be ontologically transparent, i.e. there is no gap between the idea and the thing it is about (cf. Wittgenstein’s Tractatus picture theory, where we have a one-one correspondence between words and objects).

In order to sustain Descartes’ argument about the mind-body distinction, the idea of the mind and the idea of the body must be primitive.

That is, they cannot derivate (by abstraction) from other more basic and primitive ideas.

[T]he idea I have of something is not and idea made inadequate by an abstraction of my intellect. I derive this principle purely from my own thought or awareness. I am certain that I can have no knowledge of what is outside me except by means of the ideas I have within me … But I think also that whatever is to be found in these ideas is necessarily also in the things themselves. So, to tell whether my idea has been made incomplete or inadequate by an abstraction of the mind, I merely look to see whether I have derived it, not from something outside myself which is more complete, but by an intellectual abstraction from some other richer or more complete idea which I have in myself … [T]he idea which I have of a thinking substance is complete in this sense, and that I have in my mind no other idea which is prior to it and joined to it in such a way that I cannot think of the two together while denying the one of the other. (Letter to Gibieuf 19 Jan. 1642; CSMK III: 201-2)
We can even grant Arnauld that, of necessity, one’s mind coexists with one’s body, i.e. that they are a union inside a human being.

Yet we can maintain that they are different: the mind is a thinking thing while the body is an extended thing. As such they are different substances in which different attributes inhere.

Thus even if it is not really/actually possible for the mind to exist without the body it is logically possible—there is a possible world in which the mind exists without the body. While the mind is essentially thinking, the body is not. They are thus numerically distinct.

If one entertains a primitive idea of the mind being essentially thinking and of the body not being essentially thinking, then the mind differs from the body.
  • The idea of the mind reflects that the mind really is: it is transparent, a de re idea. Descartes is assuming that when one imagines/thinks about/… one’s own mind one has direct access to it. In that case, what one is imagining/is having an idea of/…, is really what it is. We cannot divorce, as Arnauld’s argument seems to suggest, the what it is (the res) from its idea. In short, there is no gap between the idea of mind and the mind. Primitive ideas are directly representative.
There seem to be no difference between the mind (as a res) and its phenomenological character.

The exercise involved in thinking about one’s own mind is radically different from the exercise involved in thinking about an external object.

Two distinct objects/substances (e.g.: XYZ vs. H2O) may instantiate the same phenomenological properties. This is never the case when thinking about the mind.

the union between mind and body
The Union Between Mind and Body
  • Mind-Body Unison

I am not merely present in my body as a sailor is present in a ship, but that I am very closely joined and, as it were, intermingled with it, so that I and the body form a unit. If this were not so, I, who am nothing but a thinking thing, would not feel pain when the body was hurt, but would perceive the damage purely by the intellect, just as a sailor perceives by sight if anything in the ship is broken. … These sensations of hunger, thirst, pain and so on are nothing but confused modes of thinking which arise from the union and, as it were, intermingling of the mind with the body. (Sixth Meditation; CSM II: 56)

The main question, though, concerns the manner in which the mind is related to the body.

Descartes seems to give contrasting (contradictory?) answers.

On the one side, he said the soul resides in the brain (the pineal gland) and on the other side he said that it is coextensive with the body.

It must be realised that the human soul, while informing the entire body, nevertheless has its principal seat in the brain; it is here alone that the soul not only understand and imagines but also has sensory awareness. (Principle of Philosophy 4. 189; CSM I: 279-80)

My next observation is that the mind is not immediately affected by all parts of the body, but only by the brain, or perhaps just by one small part of the brain, namely the part which is said to contain the ‘common’ sense. (Sixth Meditation; CSM II: 59)

These statements suggesting that the mind-body union is guaranteed by the pineal gland seem to contradict the following

[C]lothing, regarded in itself, is a substance, even though when referred to the man who wears it, it is a quality. Or again, the mind, even though it is in fact a substance, can nonetheless be said to be a quality of the body to which it is joined. … This is exactly the way in which I now understand the mind to be coextensive with the body—the whole mind in the whole body and the whole mind in any of its parts. (Sixth Set of Replies; CSM II: 297-9)

How, though, can a non extensive substance (the mind) be coextensive with an extensive substance (the body)?

Descartes is aware of this problem.

Even though the mind is united with the whole body, it does not follow that it is extended throughout the body, since it is not in its nature to be extended, but only to think. (Fifth Set of Replies; CSM II: 266)

30. Thesoul is united to all parts of the body conjointly

But in order to understand all these things more perfectly, we need to recognize that the soul is really joined to the whole body, and that we cannot properly say that it exists in any one part of the body to the exclusion of the others. For the body is a unity which is in a sense indivisible because of the arrangement of its organs, these things being so related to one another that the removal of any one of them renders the whole body defective. And the soul is of such a nature that it has no relation to extension, or to the dimensions or other properties of the matter of which the body is composed: it is related solely to the whole assemblage of the body organs. This is obvious from our inability to conceive of half or a third of a soul, or of the extension which a soul occupies. Nor does the soul become any smaller if we cut off some parts of the body, but it becomes completely separate from the body when we break up the assemblage of the body’s organs.

31. There is a little gland in the brain where the soul exercises its functions more particularly than in the other parts of the body

We need to recognize also that although the soul is joined to the whole body, nevertheless there is a certain part of the body where it exercises its functions more particularly than in all the others. It is commonly held that this part is the brain … because the sense organs are related to it ... the innermost part of the brain, which is a certain very small gland situated in the middle of the brain’s substance and suspended above the passage through which the spirits in the brain’s anterior cavities communicate with those in its posterior cavities. (The Passion of the Soul; CSM I: 339-40)

Sameness of Body

Existence thorough time: our body keep changing, yet it is the same as the one we got in our infancy.

That remains the same, though, are not the qualitative properties but its numerical identity. The latter is granted by the soul. The numerical identity of one’s body rests on the identity of one’s mind.

But when we speak of the body of a man, we do not mean the determinate part of matter, or one that has a determinate size; we mean simply the whole of the matter, or one which is united with the soul of that man. And so, event through the matter change, and its quantity increase or decrease, we still believe that it is the same body, numerically the same body. So long as it remains joined and substantially united with the same soul … there is no longer in them any part of the matter which then belonged to them and even though they do not have the same shape any longer; so that they are only numerically the same because they are informed by the same soul (Letter to Mesland 9 Feb. 1645; CSMK III: 243)
In the same letter Descartes recognises the ambiguity in the world ‘body’

I consider what exactly is the body of a man, and I find that this word “body” is very ambiguous. When we speak of a body in general, we mean a determinate part of matter, a part of the quantity of which the universe is composed. In this sense, if the smallest amount of that quantity were removed, we would judge without more ado that the body was smaller and no longer complete; and if any particle of the matter were changed, we would at once think that the body was no longer quite the same, no longer numerically the same.(Letter to Mesland 9 Feb. 1645; CSMK III: 242-3)

In the Meditations ‘body’ is defined generally.

[[B]y a body I understand whatever has a determinate shape and a definable location and can occupy a space in such a way as to exclude any other body; it can be perceived by touch, sight, hearing, taste or smell, and can move in various ways, not by itself but by whatever else comes into contact with it. For, according to my judgement, the power of self-movement, like the power of sensation of thought, was quite foreign to the nature of a body. (Second Meditation CSM II: 17)

descartes error
Descartes’ Error
  • Feelings (cf. Damasio. 1994. Descartes’ Error)

It is wrong to consider the working of the brain and mind as separate from the working of the body.

The mind is part and parcel of the body.

E.g.: background feelings, i.e. the underlying awareness of the state that your body is in.

Background awareness depends on the various neuronal and hormonal signals arising from the body organs (skin, hearth, …) that are sent to and processed by the brain.

These signals provide a continuous update on the changes that our body state undergoes.

These background feelings provide our sense of ‘self’.

We process information emanating from our entire body.

Hence, we wouldn’t be the same person if our brain were transplanted in another person.

For the body would provide different information.

On top of background feelings we also have stronger feelings arising when we experience emotions in response to particular events.

New born babies tend to show only primary emotions (e.g. fear) which are innate and pre-organized.

As we grow we develop and make more use of secondary emotions which are primary emotions tempered by experience.

Emotions become associated with particular experiences. Thus their link with learning.


Are neurotransmitters produced in the brain.

They are also active in the human immune system and endocrine system.

Hence, they participate in the constant relationship between the brain and the body.