However, there are numerous beliefs that his argument leaves unchallenged. When we dream, although the particular beliefs we form ("I am falling from an airplane.") are often false, the materials for our dream (airplanes, physical objects) come from things we experience when waking, and we can still rest assured that some of these things exist. Therefore, the dreaming argument leaves unchallenged our belief in general truths about the world (the belief that we have hands and what these hands do for us). One of the reasons Descartes believed his mind to be essentially non-physical is that he found himself able to doubt the existence of all physical objects (even his own hand) but could not doubt that he was a thinking being (Williams, 1998). Descartes also believed that, in contrast to the physical world, the mind was an indivisible unit.

Even Descartes realized that mind and body were unable to operate in isolation. If I put my hand into a fire, a physical change in temperature results in a mental change -- pain. I would then immediately think, "I need to move my hand away from the fire." This thought results in a physical change -- I move my hand from the fire. Descartes describes the body and mind as "intermingling" to create an apparent unit.

Descartes stressed that we all have the ability to doubt. Therefore, we have the power to doubt everything, including the entire world in which we...

However, he believed that the one thing we cannot doubt is our mind. He said that while we doubt, we must exist. "Cogito, ergo sum," Descartes said (Williams, 1998): I think, therefore I am. And the thinking thing is our mind.
Descartes then doubts the existence of God and the reliability of "clear and distinct ideas," and then our bodies (including our hands), and then the world around us (Williams, 1998). However, his argument has a major gap. He has concluded that there are two distinct substances: mind and body. Mind is comprised of thought, body by extension. Mind has no size or shape or location in space, and body is physical and exists purely in space and time. These things must interact with one another, though, as when I put my hand in a fire, my mind causes me to feel pain. So mental decisions can result in physical movement.

Descartes introduced us to a world of constant questioning. He taught us to question even the obvious, such as "is this my hand?" While I like the idea of doubting everything, I feel that I have enough evidence to believe that my hands exist.

Bibliography

The President and Fellows of Harvard College. (2002). Descartes' First Meditation. Retrieved from the Internet at http://www.courses.fas.harvard.edu.

Williams, Bernard, "Rene Descartes," Encyclopedia of Philosophy, Vol. 2, pp. 344-354.