Descartes’ philosophy was well known by the 18th century and was used primarily by the founders of the scientific revolution. Georges Lemaitre used Descartes’ debate method in his study of wave mechanics. Joseph Butler strongly criticized Cartesianism and stated that Descartes was forced to conclude that the mind is simply a material function of the brain and body, and argued that Descartes had no legal basis to deny the existence of spirits because many of the great writers of the Catholic Church have argued. However, the classical concept of Descartes as a proto-scientist was discredited by Immanuel Kant, a German philosopher who worked with clearly anti-Cartesian views.
Descartes’ philosophy focused on the concept of dualism, and his goal was to arrive at an explanation of the nature of mind and how it works. It was based on the idea of dualism, the distinction between physical and mental, or between mind and body, as opposed to a consistent monistic science. In the second meditation, Descartes argues that when people discuss something with another person, the way they speak and move is determined by the body, whereas the mind is associated with thoughts. In Meditation Three, Descartes discusses the purpose of the mind, claiming that it is an impartial observer who collects and displays information.
Descartes suggested that the mind has the following characteristics:
the soul (consciousness) is divided into two parts: the intellect (besides the higher thought) and the body;
mind and body are separate but not different;
the mind has a twofold power: reasoning and perception;
there is one mind (mind and soul), but two bodies, one of which is immaterial;
the mind can imagine a material body and use it as if it were its own, but cannot cause it to appear;
mind and body are separate and yet indistinguishable from each other, so the mind does not belong to the body, and yet the body does not belong to the mind.
Descartes further argued that when people imagine the body, they represent it in terms of its materiality (it has bones and flesh). When they imagine mind, they consider it intangible. Therefore, the mind, says Descartes, should be considered as possessing the same qualities of thought and perception as the material body, and the mind and the material body were created by people, since they were created by God. Descartes also argues that mind and body can be detached and then put back together. This idea, known as dualism, was later taken up by later philosophical systems such as determinism and materialism.