Rene Descartes – Meditations on First Philosophy

Roadmap of the Meditations:


Meditation I

"once in my life I had to raze everything to the ground and begin again from the original foundations, if I wanted to establish anything firm and lasting in the sciences." (59)

The Key Question:  Of what can I be certain? That is, are there any certain foundations upon which I can build knowledge?
"to bring this about I will not need to show that all my opinions are false, which is perhaps something I could never accomplish. But reason now persuades me that I should withhold my assent no less carefully from opinions that are not completely certain and indubitable than I would from those that are patently false. For this reason, it will suffice for the rejection of all of these opinions, if I find in each of them some reason for doubt." (59)

Instead of considering individual beliefs one by one, he tries to introduce this doubt by attacking "those principles which supported everything I once believed." (60)

What principles?  E.g., My senses are reliable.  I am awake now.
Level One:  Sensory Doubt
"whatever I had admitted until now as most true I received either from the senses or through the senses."

But sometimes our senses deceive us. Does this constitute a good reason for disbelieving the senses?

Not in general. "even though the senses do sometimes deceive us when it is a question of very small and distant things, still there are many other matters concerning which one simply cannot doubt". (60)
  Q: Is this convincing?


Only a madman would deny that his senses tell him "these hands and this entire body are mine" (60)
 

Q: How can Descartes be sure he's not mad?


Having found the level of sensory doubt insufficient to call many of our beliefs into question, Descartes moves on.

 Level Two:  The Dream Argument
A new worry: Even if he can be sure he's not mad, his senses can't be trusted if he's dreaming. If he's dreaming, there's no good reason to think that the things he appears to sense are real.

Descartes' claim: "there are no definitive signs by which to distinguish being awake from being asleep." (60)

Q:  Is he correct?
What does this show?  If we can't be sure we're not dreaming are all our beliefs thrown into doubt? Descartes' Answer:  Even if we're dreaming, Descartes says we can still be sure that the things we're dreaming about are 'composed' of elements taken from real things.

The things we dream of "could only have been produced in the likeness of true things … therefore at least these general things – eyes, heads, hands, and the whole body – are not imaginary things, but are true and exist." (61)

He backs off from this: "although even these general things – eyes, head, hands and the like – could be imaginary, still one has to admit that at least certain other things that are even more simple and universal are true."
 

Q:  What does he have in mind?


"This class of things appears to include corporeal nature in general, together with its extension; the shape of extended things; their quantity, that is, their size and number; as well as the place where they exist; the time through which they endure, and the like." (61)
 

Q: What do all these things have in common?
"arithmetic, geometry, and other such disciplines, which treat of nothing but the simplest and most general things and which are indifferent as to whether these things do or do not in fact exist, contain something certain and indubitable. For whether I am awake or asleep, two plus three make five" (61)
But doubt doesn't come to an end here.


Level 3:  All Powerful Deceivers

"there is fixed in my mind a certain opinion of long standing, namely that there exists a God who is able to do anything". (61)

Couldn't God deceive us even about mathematics?

Q: Is 'But God wouldn't do that!' a good response?

Q: How about 'God couldn't deceive me about that'?


Every belief we have can thus be doubted. It is easy to forget this, so Descartes introduces the idea of the Evil Demon.

 
The Evil Demon: "Accordingly, I will not suppose a supremely good God, … but rather an evil genius, supremely powerful and clever, who has directed his entire effort at deceiving me." (62) Two Large Philosophical Questions:  Descartes will eventually reject the idea that nothing is certain.
(1) Is he right to do so?
(2) What can we be certain of?
[Philosophy 1200]