• Descartes believes it necessary to build a structure of knowledge on a sure foundation
• Considers contemporary knowledge to be suspect
• Only knowledge built on a foundation of certain facts is good enough
• Criterion for something being certain is that it cannot be doubted
• To doubt X does not mean to regard X as false: doubt is just a tool
• Descartes considers various aspects of reality to decide whether they can be doubted:
  • experience through the senses
  • the physical world
  • the laws of mathematics
  • the existence of God
  All of these are subject to doubt, especially if one considers the idea of a malicious demon
• But for me to doubt means that someone is doubting: even if the demon exists then I exist because I am being deceived.
• So I at least know that so long as I continue to think, I must exist

Problems

• Perhaps our minds are fundamentally incapable of grasping true knowledge
• Descartes doesn't appear to doubt his powers of reason
• The "foundational approach" may not be possible

  "We are part of the very universe we are trying to understand. We are trapped inside the system. There is no Archimedean point on which to stand to behold all of creation"