Cartesian Dualism

The world consists of two kinds of substances:

1. Material substances

2. Mental substances

Mind and bodies are substances of different kinds

Material substances

• extended

• unthinking

• spacial

• take up space

• have form

Mental substances

• think

• not extended

• don’t take up space

• emotions

• concepts

Support for Dualism: The indivisibility argument

Descartes uses the indivisibility argument to show a further difference between the mind and the brain and thereby further support his claim that the mind and the brain are not identical

A physical object is divisible into parts - halves, quarters, molecules, atoms, subatomic particles. Physical things are composite

The smaller objects that remain after each division are themselves physical. Physical things can perish

The mind is simple - it is not composed of parts. The mind is divisible into further, smaller units

The mind as an immaterial substance is immortal

What might be the basis of his belief that the mind is simple?

It is likely that this claim stems from his claim “I think therefore I am”. In knowing for certain that “I think”, what I know to exist is a single thinking thing. I am imagining that single mind exists, not a composite of smaller minds

In addition, when I wonder whether my body exists, I can do so in stages. I can enquire into the existence of my body part by part

This is not so with the mind. I either exist or I don’t; its all or nothing, not a matter of degree

Objections?

Descartes was wrong about the mind’s simplicity - multiple personality disorder and “split-brain” patients suggest that the mind is not simple

Multiple personality disorder suggest that the mind is not simple a single mind seems to have fragmented into several personalities

This suggest that the mind can be divided into smaller minds

Is MPD a convincing objection?

• MPD cases are extremely rare and difficult to confirm

• It is not clear that these cases really are cases of multiple minds existing in one body

• Many cases have been shown to be exaggerations; many MPD patients see themselves as fantasising and acting out different roles rather than “fragmenting” into different personalities

• MPD cases are subject to interpretation and that interpretation may reflect the bias of the therapist or researcher

In “split brain” patients the corpus callosum (the thick bundle of neurons connecting the two halves of the brain) has been severed

Some researchers claim that “split brain” patients behave as if there were two people living in the same body, each controlling one half of it

Is “split brain” a convincing objection?

• under normal condition, “split brain” patients behave normally. It is only under experimental conditions that they exhibit this unusual behaviour

• In addition, such unusual behaviour could be explained as a lack of coordination or general cognitive malfunctioning caused by serious injury to the brain