PHILOSOPHICAL ERRORS, LECTURE 2 – RATIONALISM
Rationalism (a modern form of idealism): whatever is clearly & distinctly known to belong to an idea can be
said of the thing; thought & reality are one; to be intelligible is to be real
I. Descartes: wants to combat skepticism, start philosophy over using mathematical method
a. Universal validity of mathematical method
i. Math is deductive, from 1st principles, from ideas to things
ii. Abstract, and sense knowledge sometimes impedes
iii. Mathematicians are interested in the true nature of the circle, as expressed in its
definition, not in a particular circle existing somewhere, so…
iv. All that can be clearly and distinctly known to belong to the idea of something can be
said of the thing
v. No room for doubt or disagreement, all is clear & distinct, and certain
vi. Mathematical statements are often self-evident
1. Self evident: predicate is contained in the subject, cannot think the opposite,
seen to be true once the terms are understood (like first principles & math)
2. Evident: evident to the senses, like the existence of the world
b. Methodic doubt
i. Tried to doubt everything that could be doubted (existence of world & his own body,
math facts, first principles) in order to discover…
ii. something so undoubtable, so clear & distinct that it could not be doubted.
iii. On this sure truth (first basic idea) he would build his philosophy
iv. Not a real doubt, but a methodic doubt
1. ..to accept nothing as true which I did not clearly recognize to be so…[and] to
accept…nothing more than what was presented to my mind so clearly and
distinctly that I could have no occasion to doubt it”
2. Doubting not as the skeptics did, but to discover the indubitable & ultimately to
dispel doubt and skepticism
c. Cogito
i.Cannot doubt that he is doubting
ii.I think, therefore I am (cogito, ergo sum)
iii. Even if I am deceived in this, I must be to be deceived!
iv. This idea of his own existence is clear & distinct (method)
v. First principle: his own existence as a thinking being
vi. “a substance whose whole essence or nature is to think”
vii. Thinking being (mind) is distinct (separate & independent) from the body
viii. And therefore immortal
ix. He seems to be presuming here that separate from the body means immaterial
x. Also he presumes that immaterial means immortal – which it does, but he has doubted
all that and can’t use it now!
xi. This independence of the soul/mind from the body established, to Descartes’
satisfaction, the immortality of the soul, but it leaves man as two unconnected things.
xii. Clearness and distinctness is confirmed as the criterion for recognizing truth
d. The Cogito implies the existence of God (proofs)
i. A Perfect Being must cause of the idea of perfection (perfect being) in me (a posteriori)
1. He is imperfect (doubts) so he cannot be the cause of the idea of a perfect being
2. Only possible cause is a perfect being
3. he doubted the principle of causality - he can’t use it now!
4. Why can’t an imperfect person have (cause) an idea of a perfect being? – it’s just
an idea after all!
5. There is a difference between a perfect idea (of anything) - which might need a
perfect being to cause it – and an idea – perhaps imperfect – of a perfect being.
ii. Also: idea of God (absolute perfect being) includes existence (a priori)
1. Since a non-existing perfect being is less perfect than an existing one
2. True, “existence” is part of this idea of a perfect being (such that a non-existing
perfect being is a contradiction, but this doesn’t prove there IS such a being!
3. A purely mental argument, starting & ending in the mind
4. Cannot conclude to real existence from an idea.
5. Perfect example of a rationalist argument starting with an idea
6. But just concluding to another idea (what else?)
iii. Also: my imperfection implies a perfect being
1. I must be imperfect because I can doubt
2. Therefore I do/did not cause myself (if I did I would have made myself perfect)
3. Therefore I am dependent
4. Therefore there must be a perfect being which is the cause of me.
5. This argument is a bad formulation of traditional aposteriori proofs
6. And it presupposes premises that he had doubted and not re-established
e. Proof of existence of world (first attempt in history!)
i. Idea of “extension” does not include existence as “perfect being” did.
ii. Images of things are not clear & distinct, so they do not come from the mind
iii. Where do they come from?
iv. Sensations appear to be caused by external things sensed by my body
v. If this were not so, this would be a huge deception, and
vi. God could not allow this (since He is good)
vii. so the world (and my body) exists
f. Dualist notion of man
i. “body” not contained in “mind” so they are distinct
1. This is a perfect example of idealist reasoning
ii. Connected via pineal gland
iii. This dualism is already implied in his methodic doubt
1. Disembodied mind can doubt sense evidence (since it comes from another)
2. But a body/soul unit cannot. (same being that senses & doubts)
iv. He wants to say that man is united but cannot give a reason for it
v. Descartes is known as the creator of the mind-body problem
g. Problem: the connection between “thought” & “extension” (physical reality)
i. Is thought/idea connected, related, to reality?
ii. Or, is my thinking mind connected to my reality-sensing body? (mind-body problem)
iii. It seems they are separate & unconnected realms.
iv. It seems there is a chasm between them (need to bridge it, connect them)
v. Later rationalists are all trying to correct this problem, connect them
1. Usually God is invoked to connect them
II. Critique of Descartes’ rationalism
a. His methodology is backwards: tried to go from thought/ideas to reality.
b. Doomed to failure because asked a false question (how do you go from thought to things?)
c. Different sciences have different objects and methods – you can’t just apply the method of one
science to the objects of another
i. “mathematicism:”
d. He wants self-evident certitude in areas where it cannot be had
e. Universal sense skepticism is self-contradictory
i. since you only know of sense error through knowing sense truth, it can’t all be an error.
ii. It is also impossible for man (body & soul) - Only possible for disembodied “mind”
iii. Called into question what is most evident: things are!
iv. Denied evidence of senses, wil not be able to prove that anything (God or world) is
v. Retreated into the mind – we know “ideas” rather than “things.
f. Existence of the world is evident – does not need to be proved & can’t be
g. Man is not two things, but one united being
h. Thought and reality are not identical – reality is prior, thought is about reality.
i. Knowledge is about reality; we know beings, not our ideas.
i. Knowledge is acquired through sensation; it is not innate
j. Too-narrow pre-definition of knowledge (clear & distinct, undoubtable)
i. Surely everything else (not clear & distinct) is not just opinion?
k. Led to skepticism
i. Knowledge not related to reality, can’t really know reality
ii. Doubted the existence of the world, encouraged universal sense skepticism, told
everyone it had to be proved, and then failed at it!
l. Led to dualism & materialism
i. Separated soul & body: if soul without body, why not body without soul?
m. Led to atheism
i. failed to prove the existence of God,
ii. his ontological argument viewed by later thinkers as typical of all proofs (and invalid!)
iii. denied the world (on which proofs must be based)
iv. demanded that all knowledge be self-evident, which the existence of God is not
v. all of this led to skepticism about the existence of God and eventually to atheism
