PHIL2206 Philosophy of Mind
Week 3: Substance dualism

Substances

  1. Everything is either a particular (my pen, Sydney, your shadow, the hole in my sock), a property (being red, being a city), or a relation (loving, being in-between).
  2. Every particular is either a substance (my pen, Sydney) or a non-substance (your shadow, the hole in my sock, surfaces, edges). Substances are capable of independent existence, non-substances are not.
  3. This is a technical use of the term ‘substance’ - it is not how the term is ordinarily used.

Substance dualism

  1. According to substance dualism, (a) some substances are physical (tables, chairs, bodies), (b) some substances are non-physical, and (c) minds are non-physical substances (there may or may not be other non-physical substances).
  2. So according to substance dualism, minds are particulars which are capable of independent existence and are non-physical. Note that they can exist without bodies. In particular, my mind can exist without my body.
  3. There is also substance monism, and it comes in two varieties: substance physicalism, according to which all substances are physical, and substance non-physicalism, according to which all substances are non-physical (perhaps they are all mental). We will be considering substance physicalism (also called just physicalism) in detail in coming weeks; we will not be considering substance non-physicalism.
  4. Physical substances (e.g. my body, your body) have spatial extension and spatial location. Non-physical substances (and thus minds) have neither spatial extension nor spatial location. (We sometimes talk as if minds have spatial location.)
  5. Minds exhibit mental phenomena (have mental properties, stand in mental relations, etc.). Non-mental substances (and thus physical substances) do not exhibit mental phenomena.
  6. But wait: I have spatial extension and spatial location, and I exhibit mental phenomena (e.g. I think) - isn't this a counterexample?

    Reply: I have spatial extension and location because I have a body, and strictly speaking it is my body which has the extension and location; I exhibit mental phenomena because I have a mind, and strictly speaking it is my mind which exhibits mental phenomena.

Cartesian dualism

  1. I don't just have a mind, I am a mind - in particular, I am my mind (I am identical to it). I (my mind) am somehow united with my body to form a composite thing. I am, we might say, a ghost in a machine.

    Question: So is it me that is a person, or the composite thing that I and my body compose that is a person?

  2. Cartesian interactionism: minds and bodies can causally influence each other: my mind can cause my body to move; my body can cause my mind to exhibit mental phenomena. Ultimately it is my brain that my mind causally interacts with (more ultimately the pineal gland).

Three epistemological arguments that my mind is not my body

  1. Before considering problems for Cartesian dualism, let's consider some arguments that my mind is not my body. These could be modified into arguments that my mind is not my brain, or any(?) other physical substance. If this is right, then my mind is not a physical substance. (It leaves open the possibility that my mind is not a substance at all.)
  2. First argument:

    First version:

    1. I cannot doubt that I exist
    2. I can doubt that my body exists
    3. Therefore, I am not my body
    4. But I am my mind
    5. Therefore, my mind is not my body

    Second version:

    1. I know immediately and directly that I exist
    2. I do not know immediately and directly that my body exists
    3. Therefore, I am not my body
    4. But I am my mind
    5. Therefore, my mind is not my body

    (Note that here we are appealing to Leibniz's law: Necessarily, for all x and y: if x is identical to y then for all properties p: if x has p then y has p.)

  3. Second argument:

    Strong version:

    1. My mind is transparent to me
    2. My body is not transparent to me
    3. Therefore, my mind is not my body

    Weak version:

    1. Some aspects of my mind are transparent to me
    2. No aspect of my body is transparent to me
    3. Therefore, my mind is not my body

  4. Third argument:
    1. I have privileged access to my mind
    2. I do not have privileged access to my body
    3. Therefore, my mind is not my body.
  5. We need to be wary of these three arguments. There is something wrong with the following argument, and maybe the same thing is wrong with the three above: Lois knows that Superman is a superhero; Lois does not know that Clark Kent is a superhero; therefore, there is a property p such that Superman has p but Clark Kent does not - being known by Lois to be a superhero; therefore, Superman is not Clark Kent.

Four metaphysical arguments that my mind is not my body

  1. First argument:
    1. It is part of my body's essential nature to have spatial extension and spatial location
    2. It is not part of my essential nature to have spatial extension and spatial location
    3. Therefore, I am not my body
    4. But I am my mind
    5. Therefore, my mind is not my body
  2. Second argument:
    1. I am not physical

      Argument:

      • Everything is such that: if it is physical then it is essentially physical
      • Therefore, if I am physical then I am essentially physical
      • But I am not essentially physical (I might have not been physical - I might have not have had a body, in which case I would not have been physical)
      • Therefore, I am not physical

    2. My body is physical
    3. Therefore, I am not my body
    4. But I am my mind
    5. Therefore, my mind is not my body
  3. Third argument.
    1. I existed in 1995
    2. My body did not exist in 1995 (why not?)
    3. Therefore, I am not my body
    4. But I am my mind
    5. Therefore, my mind is not my body
  4. Fourth argument.
    1. If I am my body then I am necessarily my body (Kim gives an interesting argument for this)
    2. But I am not necessarily my body (I might have had no body, or had a different body)
    3. Therefore, I am not my body
    4. But I am my mind
    5. Therefore, my mind is not my body

Cartesian dualism and the problem of causation

  1. According to Descarte's interactionist version of substance dualism, minds can causally interact with physical substances (most notably with brains and bodies).
  2. But if minds are non-physical substances, and so without spatial extension or spatial location, then how can this be? How could a non-physical mind cause changes in a physical body, and how can a physical body cause changes in a non-physical mind? There is a challenge here for Cartesian dualism - to explain how this causal interaction is possible.
  3. Perhaps we can make the challenge even more pressing. According to modern physics, for one thing x to causally influence another thing y, there needs to be a flow of energy from x to y, or a transfer of momentum from x to y. How could anything flow from something outside of space to something inside of space, or vice-versa? And for something to have momentum it needs to have both mass and velocity, but how could a non-physical mind have either of these two things?

    But why should the laws of physics be expected to apply to non-physical things?

  4. How can there be causal interaction between my mind and my body? According to Kimcartes, because my mind and my body are united. The fact that they are united is a primitive fact, one that we can appeal to when giving explanations, but not one that can itself be explained.
  5. But, Kim asks, why is my mind united with my body and not yours? Kim answers: because it is my body and not yours that my mind directly causally interacts with (even if it can causally interact with your body it can only do so indirectly, by first causally interacting with mine). So it seems that the fact that my mind is united with my body can be explained, and it can be explained by appealing to the fact that my mind directly causally interacts with my body. It would be circular to try to go on and explain the fact that my mind can causally interact with my body by appealing to the fact that my mind is united with my body.

Give minds spatial location?

  1. Maybe we can make the idea of causal interaction between minds and bodies more plausible by putting minds back into space - by allowing that they can have spatial location. It might be going too far to give them spatial extension as well, without giving up the central claim of substance dualism that minds are non-physical. But perhaps we can give them spatial location?
  2. But this raises other challenging questions:

The existence of minds

  1. Even if Cartesian dualism faces insurmountable problems, we need not give up on the idea that there are such things as minds. Perhaps they are indeed substances, just not non-physical ones. Perhaps minds are just brains - perhaps my mind just is my brain. Or perhaps minds are not substances at all - perhaps a mind is a kind of behaviour (like a nice golf swing), or a kind of functional role (like a rugby position), or something else...