When Réne Descartes (1596-1650) made his pronouncement “cognito ergo sum” he asserted that there was one thing of which he was certain and indubitable and that was that the mind is better known than the body and, therefore, must be distinct from the body[1]. Descartes argued that the body is an ‘automaton’ which, with sufficient knowlege, even its complex behavioural responses could be explained in purely mechanical terms.[2] However, he went on to say that what could not be explained mechanistically was the human capacity for thought[3]. Therefore, he compounded the nature of humanity into two distinct substances, ‘an incorporeal spirit and a purely mechanical body’[4].  This essay will attempt to answer why Descartes thought that we must understand the mind and the body as different substances and whether his argument was valid in relation to the later physicalist account of the mind and body.

Descartes decided that one of the first steps of metaphysics was ‘to lead the brain away from the senses’ so that innate reason would allow us to ‘penetrate the secrets of the most recondite sciences’[5]. So he goes on to supposing that he possesses no senses in order to ascertain what is certain and indubitable[6]. Descartes determined that there was a singular part of reality that could not be accounted for. As a result, he theorised that all other matter is essentially a substance that has an extension in space but this other reality was a different substance that had no extension and whose essential feature was thought[7].

A substance, according to Descartes, is something that requires nothing else in order for it to exist and the substance of the mind is defined as the mind’s ideas[8]. For Descartes the mind was a substance that is whole and indivisible[9]. It does not receive impressions from other parts of the body but only through the brain[10]. Descartes rationalised that the essential feature of the mind is that it is a thinking thing[11]. This thinking thing doubts, understands, conceives, affirms, denies, wills, refuses, imagines, and perceives[12]. He added that the human mind is not extended in length, breadth or depth and does not participate in the properties of the body[13]. Therefore, the substance of the mind is thought and as a thinking, unextended thing it is distinct from the body which is a non-thinking, extended thing[14].

Descartes wanted to know whether the mind is so dependent upon the substance of the body that it could not exist without it[15]. Defining the substance of the body, Descartes described it as something that can be terminated by a certain figure, comprised in a certain place and able to fill a certain space so as to exclude all other bodies from that space. The body can be perceived by its senses, can be moved in different ways but not within itself[16]. When considering whether the mind is different from the corporeal nature of the body[17], he stated that the mind turns upon itself to contemplate an idea and it turns towards the body to contemplate an object[18]. Descartes concluded that the body is closely conjoined with the mind but is distinct from it because it is an extended and unthinking thing. Furthermore, the mind is so distinct from the body that it can exist without it[19].

Descartes argued that the mind can exist without the body because these two substances are opposite from one another and can be understood independently[20]. This notion of the mind and body being distinct from each other created what is known as the mind-body problem. This is the dilemma created by the notion that the mind only has modes of understanding, such as will and sensation, while the body has modes such as shape or motion, yet neither has the modes of the other. This then raised the question of how the two different substances causally related[21]. However, Descartes, in his final writing Passions of the Soul[22], argued that the mind and body can be considered whole through the ‘primitive notion of the union of body and soul’[23].

Descartes’ argument that the substance of the mind was indivisible is disproven by modern scientific methods. The mind is the electron activity within the brain. Electrons are bits of matter that have no extension or spatial position[24]. As the activity of the mind can be traced using these electrons, it would be reasonable to assert that after death these electrons would disperse as there would be no body activity to keep them organised. Additionally, his defence of the mind-body causality problem is vague and therefore uncertain, yet it would be unlikely that he considered that the two substances would not act in conjunction.

In comparison to Descartes’ distinction between the substances of the body and the mind, physicalists believe that only the physical world exists and can only be studied through objective science.  The theory relates to mental states as a system of causes, such as pain through hurting one’s body. Thomas Nagel notes that although this appears to be reality, physical reality and mental reality are quite different things[25]. Paul Churchland turns to what is called the substance dualism of Descartes, explaining that Descartes, in trying to account for the conscious reason of humanity, proposed what Churchland calls ‘a radically different kind of substance that has no spatial extension or spatial positioning whatever’[26]. Churchland states that the problem with Descartes ‘mind-stuff’ is that being an immaterial substance it could have no causal effect upon the body[27].  Also, Descartes principle of divisibility of matter no longer holds with contemporary physics. Churchland gives the example of electrons, which are a point particles with no extension whatsoever[28].  However, physicalism’s main problem is that although it can explain how an organism functions it cannot explain its consciousness[29].

Over time different explanations have been made by dualists who uphold Descartes’mind-body distinction. Popular dualism which claims that the mind can interact with the brain in some way not yet understood[30] is called popular because it adheres to the theory that the mind can survive death, however there is no empirical evidence of this[31]. Property dualists  claim that mental properties are irreducible and not just organised features of physical matter[32]. However these claims are weakened by the case for evolutionary emergence, the evolution of the mind by the organisation of matter into large physical systems that have a complex internal organisation. Therefore, the mind would not have fundamental properties or could be said to be irreducible[33].

The physicalist rejection of dualism lies in the evolution of our species. For the physicalist there is no need for nonphysical substances within ourselves.  We are made of matter and that is all[34]. It must be acknowledged that the fact of the presence of electrons within the brain performing the functions of the mind does contradict the argument for the indivisibility or irreducibility of Descartes’ mind substance. Also, the result of such dualistic thinking is the privilege of the mind over the body[35]. This makes the body just a vessel that holds the mind, inviting the body to be constructed in negative terms and leading to the position of ‘biological determinism’[36].

Descartes has left  physicalists with the dilemma of not being able to account for the brain’s consciousness, its qualifiable activities or whether it survives death. However, dualism still leaves the problem of being unable to account for the interaction between the mind and the body. It becomes obvious that both the body and mind do not have privilege over the other, or are even able to act separately in any apparent way. Thus it must be stated, from his own account, that the mind-body distinction argued by Descartes is something that is neither certain or indubitable.


  1. Anderson, Nicole, “Bodies and Embodiment” in Cultural Theory in Everyday Practice, Oxford University Press, (2008), pp. 7-13
  2. Churchland, Paul M. “The ontological problem (the mind-body problem)” in Matter and Consciousness: A Contemporary Introduction to the Philosophy of Mind, (1988), pp.7-22
  3. Cottingham, John, “Backgound (extract)” in The Rationalists (1988), pp.1-17
  4. Descartes, Réne. “Meditation II: Of the nature of the human mind, and that it is more easily known than the body” in The Meditations of Descartes (1962), pp.29-41
  5. Descartes, Réne, “Meditations I – VI”, Trans. Jon Veitsch, (1901) http://www.wright.edu/cola/descartes/meditation1.html (2005)  Retrieved: 18. 4. 2011
  6. Nagel, Thomas, “The mind-body problem” in What Does It All Mean?” A Very Short Introduction to Philosophy,  (1987), pp.27-37
  7. Skirry, Justin. “Réne Descartes: An Overview”, (http://www.iep.utm.edu/descarte/#H7) (2008) Retrieved: 21. 4. 2011
  8. Townley, Dr. Cynthia, Lecture 11 , “The Cartesian Revolution” in Mind, Meaning and Metaphysics, PHI130, Macquarie University, (2011)

[1] Townley, Dr. Cynthia, Lecture 11 , “The Cartesian Revolution” (2011)

[2] Cottingham, John, “Backgound (extract)” in The Rationalists (1988): 15

[3] Ibid.

[4] Ibid: 17

[5] Ibid: 4

[6] Descartes, Réne. “Meditation II: Of the nature of the human mind, and that it is more easily known than the body” in The Meditations of Descartes (1962): 29

[7] Churchland, Paul M. “The ontological problem (the mind-body problem)” in Matter and Consciousness: A Contemporary Introduction to the Philosophy of Mind, (1988): 8

[8] Skirry, Justin. “Réne Descartes: An Overview”, (http://www.iep.utm.edu/descarte/#H7) (2008)

[9] Descartes, Réne, “Meditations VI”, Trans. Jon Veitsch, (1901)

[10] Ibid: 20

[11] Descartes, Réne. “Meditation II” (1962): 33

[12] Ibid: 35

[13] Descartes, Réne, “Meditations IIII”, (1901):1

[14] Descartes, Réne, “Meditations VI ”,((1901):9

[15] Descartes, Réne. “Meditation II” (1962): 30

[16] Descartes, Réne. “Meditation II” (1962): 32

[17] Descartes, Réne, “Meditations IIII ”, (1901):10

[18] Descartes, Réne, “Meditations V ”, (1901):3

[19] Ibid:9

[20] Skirry, Justin. “Réne Descartes: An Overview”, (2008)

[21] Ibid.

[22]Cottingham, John, (1988): 15

[23] Ibid.

[24] Churchland, Paul M. (1988): 9

[25] Nagel, Thomas, “The mind-body problem” in What Does It All Mean?” A Very Short Introduction to Philosophy,  (1987): 35

[26] Ibid: 8

[27] Ibid.

[28] Churchland Paul, M. (1988) :9

[29] Ibid: 36

[30] Ibid

[31] Ibid: 10

[32] Ibid.

[33] Ibid: 13

[34] Churchland Paul, M. (1988) : 21

[35] Anderson, Nicole, “Bodies and Embodiment” (2008): 4

[36] Ibid.