Substance Dualism

Substance Dualism Overview

  • Substance Dualism, also known as Cartesian Dualism, is the theory proposed by René Descartes stating that the mind and body are two distinct substances.
  • Dualism argues against materialism which posits on the mind being merely the brain or its functions.
  • The mind, according to substance dualism, exists independently of the physical brain.

Substances According to Descartes

  • Descartes identifies the two substances as: res cogitans (thinking substance) and res extensa (extended substance).
  • Res cogitans refers to the mind, which possesses consciousness, self-awareness, understanding, and sense of self. It can’t be physically located or measured.
  • Res extensa refers to the physical world, including the human body, which exists in space and time, has mass and can be measured.


  • Substance Dualism often includes the theory of Interactionism. Descartes believed these two substances interact with each other within the human body.
  • The pineal gland was initially suggested by Descartes to be the “seat” of this interaction, though this theory has largely been contested.

Criticisms of Substance Dualism

  • Descartes’ proposal has been subject to many criticisms from philosophers and scientists.
  • The issue of how two distinct substances, physical and non-physical, could possibly interact is known as the “mind-body problem”.
  • Gilbert Ryle criticised Substance Dualism, regarding it as the ‘category mistake’. He argued that mental states are not things but rather ways of behaving.
  • Physicalists criticise Dualism as non-empirical, as mental states cannot be measured or observed directly like physical states.
  • Occam’s Razor, the principle that the simplest explanation is most likely to be correct, is often used to argue against substance dualism due to its complexity.

Substance Dualism and Personal Identity

  • Substance Dualism argues that personal identity is rooted in the continuous existence of a non-physical mind, providing interesting discourse on themes such as life after death and reincarnation.
  • This perspective also provides room to debate concepts of free will, as mental events (choices and decisions) are seen as independent of physical events in the world.