What is res cogitans and res extensa?

Res cogitans and res extensa are two concepts in philosophy introduced by Rene Descartes, a French philosopher.

Res cogitans, also known as "thinking substance," refers to the part of reality that exists only in the mind or as a mental construct. It includes ideas, thoughts, beliefs, and perceptions. Descartes believed that the mind is immaterial and cannot be reduced to physical properties. He famously wrote, “I think, therefore I am,” to illustrate the existence of the mind as a thinking substance.

Res extensa, also known as "extended substance," refers to the part of reality that exists in the physical world and has spatial dimensions. It includes all material objects such as rocks, trees, and animals. Descartes believed that these physical objects are subject to mechanical laws of nature and can be studied through scientific observation and experimentation.

Descartes' distinction between res cogitans and res extensa had a significant impact on the development of modern philosophy and science. The concept of res cogitans influenced the fields of psychology, neuroscience, and cognitive science, while res extensa laid the foundation for modern physics and engineering.