PHLA10 – Lecture 10 Notes October 30 and November 1 , 2012
Descartes and Foundationalism
Chapter 13: Pages 156 - 169
Descartes wanted to show that the beliefs we have about the world are cases of genuine
knowledge He split them up into two categories.
1. Foundational beliefs: Perfectly solid
2. Superstructural beliefs: Count as knowledge because they rest securely on foundational
Used axiomatic geometry as a model to demonstrate this:
o Axioms (like foundational beliefs) are ‘self-evident’
They cannot be false and absolutely certain
o Theorems (like superstructural beliefs) are deduced by axioms
Follow by pure logic and inherit certainty
Method of Doubt
Descartes’ goal was to refute skepticism
He developed his Method of Doubt to determine which of the beliefs he has are foundational;
whether it is possible to doubt a proposition.
o If a doubt is possible then it isn’t foundational.
o If a doubt isn’t possible then it is foundational (indubitable belief)
Doesn’t mean that the belief is false, it just isn’t absolutely certain.
A posteriori beliefs based on whatever you observe: sense, memory, testimony, etc
o Dreaming, hallucination and illusions give reasons for putting such beliefs into doubt
A priori beliefs based upon logical or mathematical reasoning; some of which rely on memory
o Example: “2 + 2 = 4” or “A square has four sides”
o Evil Genius Argument: That an evil genius has deceived your mind to think so; there is a
“I think, therefore I exist.”
Any proposition which if you think it, it must be true Survives the Method of Doubt
First-person descriptions of the way things seem are indubitable.
Incorrigibility: We cannot be mistaken about our own mental states
o Also known as the transparency of the mental
If we are in a mental state, X, we will know we are in X PHLA10 – Lecture 10 Notes October 30 and November 1 , 2012
Descartes and Foundationalism
o Incorrigibility and transparency aren’t very plausible due to self-deception and
unconscious mental states
Example: Can you being suffering excruciating pain and not know it? Can you
believe you are suffering excruciating pain and be wrong?
Clarity and Distinctness
Some cases that made some beliefs could not be in error
Clarity: What is present and apparent to the mind
Distinctness: Every feature of the idea is clear
o Example: Belief there is a book in front of me
It isn’t clear and distinct
1. The experience of seeming to see a book
2. The idea that the book is existing in the world
Only the first is clear and distinct and is the only thing that we can know for
Rule of truth: Whatever we think of which is clear and distinct must be true
Descartes’ view of Mental Certainty
We have beliefs of solid foundation, but are they extensive enough to rest all our knowledge on
o How do we go from: “I seem to see a cat” “There is a cat”?
o Descartes thought we needed to know that God existed.
(1) If God exists and we are not able to know anything despite all the evidence
before us, God must be deceiving us.
(2) But God is no deceiver.
(3) Therefore, if God exists, we can know things
If we have done everything we should