René Descartes wrote a philosophical essay titled "Six Metaphysical Meditations". Descartes thinks about the nature of reality, knowledge, and the human mind in six meditations that make up the book. Descartes employs a process of doubt in the meditations to methodically doubt all he knows and thinks in order to arrive at certain and undeniable truths. He has said that the only thing in which he is certain is his own existence, which is summed up in the idiom "Cogito, ergo sum" or "I think, therefore I am." On top of this basis, Descartes goes on to investigate the nature of reality, positing that there are two different kinds of substance: material substance (which encompasses the physical world) and immaterial substance. He also looks at how the mind and body are related, claiming that although they are separate, they do interact.
René Descartes (1596–1650) was a pioneering metaphysician, a masterful mathematician, and a significant scientific thinker. He was primarily a mathematician throughout his life, followed by a natural scientist or "natural philosopher" and a metaphysician. He created the methods in mathematics that allowed for algebraic (or "analytic") geometry. He co-formulated the sine rule of refraction, created a significant empirical account of the rainbow, and proposed a naturalistic explanation for how the earth and planets formed in natural philosophy, among other notable accomplishments. A world of matter with a few basic properties and interacting according to a few universal principles was his new conception of the natural world, which has influenced how we think about it even today. Descartes created the contemporary interpretation of the mind-body problem by proposing that this natural world had an immaterial mind that was directly tied to the brain in humans. He offered proof for the existence of God in metaphysics, demonstrating that the nature of matter is an extension and the essence of the mind is thought. Early on, Descartes asserted that he had a unique method, which he later claimed to have used in metaphysics, natural philosophy, and many applications of mathematics.
