Phil 305/pols 370 Notes #2 Page René Descartes (1596-1650)



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PHIL 305/POLS 370 Notes #2 Page


René Descartes (1596-1650)

  1. Descartes was a French mathematician, scientist and philosopher

  • his most famous books are:

  • Discourse on Method (1637)

  • Meditations on First Philosophy (1641)

  • Principles of Philosophy (1644)

  • his mathematical discoveries include the Cartesian coordinate system with its three axes (x, y & z), and analytical geometry, which allows regular geometric curves to be analyzed mathematically

  • these two discoveries allowed regular motions in space to be calculated; the subsequent discovery of calculus by Newton and Leibniz allowed irregular motions to be calculated

  • these advances led to the mathematization of physics and allowed accurate predictions to be made about physical movements

  1. in an early work called Le Monde (“The World”), Descartes had proposed a deterministic system of physics that promised to explain all the motions of material objects

  • the book was not published until after his death because he was afraid of being arrested like Galileo

  • according to the physics of Descartes, the motions of the universe are caused by vortices (like whirlpools) in the ether that fills space (he did not think a vacuum could w\exist)

  • Descartes’ system of physics was eventually rejected in favor of Newton’s system, but both systems were deterministic

  1. in his epistemology, Descartes was a rationalist rather than an empiricist

  • in epistemology (the study of the nature and acquisition of knowledge):

  • rationalism is the theory that sensory perceptions are unreliable and that knowledge begins only with the use of reason

  • empiricism is the theory that knowledge always begins with perception, which is largely reliable

  • a third theory, called skepticism, is that we never gain real knowledge and that our beliefs are always just our beliefs

  • but one may always ask the skeptic, are some beliefs more believable than others?

  • if so, there must be non-arbitrary criteria that distinguish better beliefs from worse ones, which means that the movement toward knowledge must be possible

  1. Descartes thought we can never trust sensory perceptions as the starting point in the search for truth

  • he said there is no way to tell whether our perceptions are true; for example, at this very moment, how do you know you're not just having a vivid dream or are hallucinating?

  • modern science fiction writers have asked similar questions:

  • how do you know you're not a brain in a vat of nutrients that is being fed information through wires by a mad scientist?

  • how do you know you’re not a robot made of biological materials that has been programmed to think you are a real person?

  • how do you know you're not just part of a computer simulation, like the Matrix?

  1. his distrust of perception led Descartes to develop the Cartesian method, or the “method of doubt”

  • this method tells us to doubt everything we think is true, except that which cannot possibly be false

  • since perception is unreliable, knowledge must instead be founded on self-evident truths, discovered by reason alone

  • Descartes claimed that self-evident truths are those that are “clear and distinct”

  • once we have found a self-evident truth, we can use reason to build knowledge upon that foundation

  1. in his search for a foundational truth upon which to build knowledge, Descartes asked himself, how can I prove that anything really exists? how can I even prove that I exist?

  • his answer: even if my perceptions and thoughts are otherwise false, it cannot be false that I am thinking, so the mere fact that I am thinking proves that I exist

  • he summarized this argument in Latin: cogito ergo sum,” which means, “I think, therefore I am”

  • although this is Descartes' most famous saying, St. Augustine (b 354) had made the same argument much earlier:

I am most certain that I am…. I am not at all afraid of the arguments of [the skeptics] who say, What if you are deceived? For if I am deceived, I am. For he who is not, cannot be deceived; and if I am deceived, by this same token I am. (Augustine, City of God)

  1. Descartes thought that upon the foundation of “cogito ergo sum,” we can build our way up to knowledge of the existence of the “external” world, or the world “outside” of our thoughts

  • the simplified steps in his argument:

  1. if you know you exist, then you know there is such a thing as existence

  2. if there is such a thing as existence, there must be such a thing as perfect existence

  3. God is perfect existence, so God must exist

  4. as a perfect being, God is not a deceiver, so the world we perceive must exist

  • this argument an example of a kind rationalism that today is sometimes called “foundationalism”

  • foundationalism is the epistemological theory that knowledge requires a basis in self-evident truth

  1. in his ontology, Descartes’ theory of reality is called mind-body dualism,

  • he said mind and matter are separate kinds of substance; today this is called “Cartesian dualism”

  • mental substance is our thoughts, which for Descartes included perceptions, feelings and acts of will

  • physical substance is defined by “extension” in the three dimensions of space

  • in today’s philosophical jargon, physical things are still sometimes defined as “having extension,” i.e. as taking up some space

  • in summary, mental reality consists of our subjective experiences, while physical reality consists of objective physical bodies

  • according to Descartes, animals do not have subjective experiences and exist only as physical bodies

  • unlike animals, human beings can think, so we belong to both realms (mental and physical) at once

  1. Descartes' theory of mind-body dualism provided him with an answer to the problem of determinism

  • his early work had described the universe as entirely materialistic and mechanistic, but he later said that when he looked back on that theory of reality, he could not find a place for humans within it

  • a purely mechanistic worldview, in which everything is ruled by laws of cause and effect, leaves no room for human freedom

  • to resolve this deficiency in his earlier one-world theory of reality, Descartes proposed his new dualistic theory of reality

  • his new theory was that we belong to two levels of reality at once: a mental world of free thought and a physical world of deterministic physics

  1. in modern terminology, Cartesian dualism is called “interactive substance dualism”

  • this means that reality consists of two kinds of substance (mental and physical) that interact with each other

  • the interactions between mind and body go in both directions:

  • the mind receives inputs from the body through sensations

  • the mind provides outputs to the body through acts of will

  • however, Descartes’ dualistic ontology lacked an adequate explanation for how these interactions could occur

  • if mind and body are separate kinds of reality, how do our sensations come into our minds from our bodies?

  • and when we choose to act, how do from our minds cause our bodies to move?

  1. later critics also argued that Descartes’ philosophy puts too much emphasis our subjectivity, because it is the only realm that we can directly prove really exists (via cogito ergo sum)

  • these critics say that mind-body dualism presents an artificial view of human experience, which is never purely subjective and is always immersed in wider context of understanding (i.e. a “world”)

  • in political philosophy, some say that Cartesianism promotes a self-centered form of individualism that ignores the social foundations of human reality

  • many of these critics are social constructionists who believe that reality is constructed communally through social interactions over time


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