PHLA10H3 Lecture Notes - Lecture 10: A Priori And A Posteriori, Foundationalism
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PHLA10 – Lecture 10 Notes October 30th and November 1st, 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