Philosophical History of Dualism

The philosophical history of Dualism—the idea that reality consists of two fundamental kinds of substances or principles, notably mind and body, or mental and physical—is rooted, in the West, in Plato and early Christian thought. Plato (c. 428–348 BCE) taught that an immortal soul is distinct from the mortal body; the body is a prison, the soul seeks to return to the realm of Forms, its true home—thus, substance dualism, soul and body.

Early Christian thinkers, such as Augustine (354–430 CE), influenced by Neoplatonism and dualistic interpretations of certain biblical verses, considered the soul as superior and eternal, the body as lesser and corruptible, even though created by God. (The lack of dualistic verses in the Hebrew Bible and the tension between a resurrection and an immortal soul in the Christian tradition require complex analysis.)

Classical and Early Christian Roots

René Descartes (1596–1650), considered the father of modern dualism, provides clarity to arguments in support of substance dualism.

• The Mind (res cogitans): Thinking, non-extended substance.
• The Body (res extensa): Extended, non-thinking substance.
• Well-known for “Cogito, ergo sum” (“I think, therefore I am”).

Descartes made some outlandish (to our sensitivities) statements—the pineal gland in the brain is the seat of the soul, and non-human animals are automata without consciousness, relegating them to be soulless machines without minds (a view that almost every dog owner would roundly reject). Nonetheless, by providing lucid descriptions of dualism, he established a benchmark for modern understanding.

Modern Developments and Challenges

As such, most Western elites, as well as almost all Western citizens, subscribed to philosophical dualism—until dualism was eclipsed by the rise of materialism/physicalism (exemplified by neuroscience). In this context, dualism has had an ‘interaction problem’—how could mental states affect physical states (brain), even though they are of a completely different kind, and the physical arena is closed?

Today, while a majority of US and Western citizens believe in dualism, most philosophers of mind do not. In recent decades, David Chalmers has resurrected dualism, framed with a contemporary form (e.g., naturalistic dualism).