PHI 205 Lecture Notes - Lecture 13: Dream Argument, Mental Body
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Rationalist Thought
• Knowledge a priori vs. knowledge a posteriori
• Descartes is looking for knowledge that can be a priori
Descartes’ First Meditation
• The principle of reasonable doubt:
o “Reason now leads me to think that I should withhold my assent from opinions
which are not completely certain and indubitable just as carefully as I do from
those which are patently false. So, for the purpose of rejecting all of my opinions,
it will be enough if I find in each of them at least some reason for doubt”
• Is there some reason to doubt that these “hands or this whole body are mine”?
o How do I tell if I’m just dreaming that these are my hands or if they actually are?
• The dream argument
o Main argument that Descartes uses
o Since we can’t be sure if we are awake or asleep, it is reasonable to doubt whether
are not these are actually your hands, etc.
o Any belief that would be based on considerations of the senses aren’t going to be
compatible with true knowledge
• The evil demon
o Some “deceiver of supreme power and cunning who is deliberately and constantly
deceiving me” and tricking him into thinking certain things exist in a certain way,
etc., when they actually exist in another way.
Descartes’ Second Meditation
• “…I will proceed in this way until I recognize something certain, or, if nothing else, until
I at least recognize for certain that there is no certainty.”
• What could we know, if we follow the principle of reasonable doubt and the dream
argument makes it doubtful that “these are my hands,” etc.?
o What is left, if anything, that we could know?
o Against this backdrop, Descartes tries to convince the reader that there is
something that we can know indubitably.
• The case of self-knowledge: I think therefore I am
o “I have just said that I have no senses and no body…Am I not so bound up with a
body and with senses that I cannot exist without them? But I have convinced
myself that there is absolutely nothing in the world, no sky, no earth, no minds, no
bodies. Does it now follow that I too do not exist? No: if I convinced myself of
something, then I certainly existed.”
o Says that the evil demon also proves his existence, because he must obviously
exist to be acted upon in that way.
o “I must finally conclude that this proposition, I am, I exist, is necessarily true
whenever it is put forward by me or conceived in my mind.”
o It’s indubitable that you exist if you have these thoughts
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