Rene Descartes: Philosopher and Mathematician.
Geometry was a model for knowledge
Foundationalism: an approach to thinking about the structure if all our beliefs
Philosophy is a Tree: Roots = Metaphysics
Trunk = Physics
Branches = Sciences (knowledge*)
All knowledge is founded upon metaphysics, it is constructed from the
bottom up, we have to get back down to the principles to understand
Descartes using Methodological Doubt can systematically examine all beliefs and
determine which ones are the ‘axioms’ – foundational beliefs – for our
Descartes’ Method of Doubt Test:
Is it possible to make up a story in which both… :
(1) I believe P
(2) P is false.
If yes -> P fails the MDT and the belief is not foundational.
If no -> P passes the MDT and the belief is foundational. (Impossible to
Note: Think of Non-Fictional as real. Terms are backwards. Non-possible P’s are real (foundational), they pass the MDT
All a posteriori beliefs fail the MDT – beliefs based on senses are subject to MDT
I’m on the moon right now…
All first person psychological states pass the MDT
I seem to be in philosophy class right now…
Note: Sometimes a priori beliefs – 2+2=4 – fail MDT like: an evil all-powerful being is bent on deceiving me
Descartes Concludes: I doubt, I am, I’m not, I exist are claims that pass the
Method of Doubt Test the foundation of all knowledge. You also cannot be wrong about what you think you want and what you think is true – The