Cogito, ergo sum - "I think, therefore I am."
Good sense is the most fairly distributed thing in the world; for everyone thinks himself so well supplied with it that even those who are hardest to satisfy in every other way do not desire more of it than they already have." from Discourse on the Method (1637)
Descartes in Wikipedia, Sanford Encyclopedia of Philosophy, Internet Encyclopedia of Philosophy
Noam Chomsky on Descartes' World as a Machine & the attack on the Scholastics' view of science. 16:00 video
Most Important Works
Discourse on the Method (1637)
Meditations on First Philosophy (1641)
w/ objections (from Thomas Hobbes, Pierre Gassendi, Antoine Arnold, and others)
Online: First Meditation, Second Meditation, Third Meditation,
Fourth Meditation, Fifth Meditation, Six Meditation
Principles of Philosophy (1644)
Descartes' main influence in philosophy were in epistemology and philosophy of mind. In mathematics, Descartes is important for his Cartesian Coordinate system the combined algebra and Euclidean geometry.
Descartes was a rationalist in much the way Plato was a rationalist. He begins the modern debate on whether humans are born with innate ideas in their minds (Several decades after Descartes, John Locke, an empiricist, will be the first in the modern era to follow Aristotle in saying that there are no innate ideas).
Biography
Descartes was born in France and educated by the Jesuits in his native France, earning a law degree at age 20. Then he soldiered for four years, afterwards he traveled to Holland, Germany and Italy. In 1628 he moved to Protestant Holland where he lived to almost the end of his life, through which he remained a Catholic.
After moving to Holland, he did work in mathematics, optics, and meteorology before turning to philosophy (his work in mathematics is seen as the biggest influence on Isaac Newton).
The publication of Discourse on the Method, 1637, is usually seen as the first work of modern philosophy because it explores the inner workings of the mind by exploring consciousness. He died of pneumonia in 1650 while tutoring in the court of Queen Christina of Sweden.
Cartesian skepticism - systematic doubt
Descartes' desire for a methodological science that was grounded in certainty led to his famous thought experiment.
Descartes would doubt everything he knew. Believing he was dreaming or tricked by an evil demon into believing that his ideas of an external world was created by his untrustworthy senses, he turns to meditating on the thoughts of his mind...
"I rejected as false all the arguments I had so far taken for demonstrations. Finally, considering that the very same experiences [thoughts] as we have in waking life may occur also while we sleep, without there being at that time any truth in them, I decided to feign that everything that had entered my mind hitherto was no more true than the illusions of dreams. But immediately upon this I noticed that while I was trying to think everything false, it must needs be that I, who was thinking this, was something. And observing that this truth 'I am thinking, therefore I exist.'"
Epistemology:
Innate ideas - "clear and distinct" idea implanted by God. One such idea was that of perfection. For Descartes, only something that is perfect could implant the idea of perfection in the mind and the only thing that is perfect is God. And God, being perfect, must be good. A good God would not deceive me by implanting false ideas in my mind. So clear and distinct ideas must be certain.
Descartes held that objects and functions mathematics were both innate, and also clear and distinct, ideas; e.g. it could not be doubted that 2 + 2 = 4.
Three clear and distinct ideas the mind has are size and shape (in three dimensions) and motion (these belong to field of geometry). These are the "primary qualities" of objects. Descartes believed they were caused by the external world. But other sensory perceptions like weight, colors, smell, tastes, heat and cold, are not clear and distinct (these are "secondary qualities"). So we can doubt that they belong to the external world but believe they are internal to the mind.
The concept of innate ideas, or mental processes built into the mind, still has currency today. Noam Chomsky has argued that the structure of grammar is "hard-wired" into our brains. The idea is that the rules of grammar are so complex that, if they had to be taught, many years would be needed to teach a child to learn to speak. But because the syntax of language is built into our brains, all a child needs to learn is the words and the brain knows how to structure sentences using them.
Mind/Body (Cartesian) Dualism:
In philosophy of mind, Descartes believed that the body was a physical substance (it has extension), but the mind (thoughts) was not (a non-extended) substance. The mind could think, the body could not. The body could be destroyed, the mind (or soul) could not. "Thought" for Descartes was any mental phenomena; doing arithmetic, feeling pain, hearing music, hoping, fearing, fantasying, etc; it was anything that could be experienced by consciousness.
Descartes claimed that extended objects (material objects - everything in the physical universe) were mechanical; they were machines. This included the human body. But, minds/souls and God were not machines. The 20th century philosopher Gilbert Ryle dubbed the Cartesian mind "the ghost in the machine." Machines are subject to laws of science, but minds are not.
The most famous 17th century opponent of dualism was Baruch Spinoza. Thomas Hobbes was another.
Cartesian Consciousness:
In psychology, Descartes substituted consciousness for rationality. The ability to self-reflect, and not rational thought, was what differentiated humans from all other living things (thus he did not have to disagree with Montaigne's claims that dogs were rational animals).
The modern philosophical mind/body problem goes back to Descartes. The dualist needs to answer this question: how can a non-extended (a non-physical) substance like a mind make an extended (a physical) object move? How can a thought to make my arm go up make my arm go up? Descartes believed the mind was connected to the body through the pineal gland, which we now know to be untrue. The modern problem is "how does the brain give rise to consciousness?"
Descartes' influence:
"Western philosophers, since the time of Descartes and Locke, have struggled to comprehend the nature of consciousness and identify its essential properties. Issues of concern in the philosophy of consciousness include whether the concept is fundamentally coherent; whether consciousness can ever be explained mechanistically; whether non-human consciousness exists and if so how can it be recognized; how consciousness relates to language; whether consciousness can be understood in a way that does not require a dualistic distinction between mental and physical states or properties; and whether it may ever be possible for computing machines like computers or robots to be conscious, a topic studied in the field of artificial intelligence."
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