Philosophy of Mind
Introduction Dualism Behaviourism Identity Theory Functionalism Dennett


  Psychophysical Parallelism






Non-Cartesian Dualism
  Further Reading


The problem with Descartes' definition of mind and body is that he seems to be describing two mutually exclusive substances. If, in every respect, matter differs from mind, how are the two meant to interact? Descartes needs to explain this because, unlike other theories which we will look at later, there is meant to be a causal interaction between the two substances – in other words, mind influences matter and vice versa. This is called interactionism.

However, the difficulty here is how a material thing – our body – can be influenced by a non-material thing – our mind. By Descartes’ definition mind is immaterial, having no dimension, mass, etc. But then how can something without any physical effects influence a physical thing? According to current scientific thinking, physical objects are only affected by physical forces. Even if we think in terms of atoms, molecules or particles, we are still talking about things with dimension and mass – however small. In this sense, the material world is a closed circuit of cause and effect.

Descartes’ response was to suggest that the two substances meet in a part of the brain called the pineal gland. His reasons for choosing this seem to have been that the gland in central (unlike the other parts of the brain which are bilateral – mirrored on each side) and that it does not occur in animals. This latter fact was understood by Descartes as relating to the presence of a soul in humans and not in animals, whom he considered mere machines. However, modern research has also found a similar gland in mammals and lower vertebrates.