Cartesian dualism is the the idea that the human body is a mechanical object that is controlled by an immaterial mind, first proposed by seventeenth-century French philosopher René Descartes (1596–1650). It falls under the philosophical topic of mind-body dualism, which postulates that minds and/or souls are separate from physical bodies.
While Descartes's evidence for his own theories of mind-body dualism is widely accepted as defensible to at least some degree, Cartesian dualism is contested far more vigorously.
Descartes argues that the mind and body must be separate because it is possible to doubt the existence of a physical body (it may be a hallucination, a dream, etc.), but according to him, one cannot fathom the nonexistence of their own mind (a concept explored in reference to Descartes's most famous quote, "I think, therefore I am").
The extension of this idea that comprises Cartesian dualism is that consciousness is separate from a physical body, but that the two entities interact: things that happen to the physical body impact the mind, and actions of the mind impact the physical body.
Initially this may seem fairly clear-cut, but many philosophers and laypeople alike in the past four hundred years or so have countered Descartes's claim, wondering how an immaterial mind can control a physical body.
There are many questions that guide these conversations: Why do your fingers move according to your whims? If your consciousness is separate from your body, how can it control how you move? Why does your thinking become unclear or emotions become altered when you consume alcohol?
Many other resolutions are offered as well. For one, perhaps the body is controlled through an act of God. Descartes himself offered the option that there is a point of contact between the body and mind, such as the pineal gland (located between the two hemispheres of the brain). Modern medicine and neurobiology have yet to offer widely accepted insights—only more questions.