Descartes' doubting of science and mathematical reasoning is referred to as Cartesian doubt.
He found that the method was ruthless - if you doubted one scientific fact, then it led you to doubt another scientific fact, and so on.
Descartes suggested that there is no knowledge that can be guaranteed. He could not even be certain that his own body was real.
He was, however, certain that his thoughts existed.
Descartes' Cartesian doubt is a form of thinking, so trying to doubt that you are thinking by thinking is impossible.
With this insight, Descartes coined his famous phrase, 'Cognito ergo sum,' which is Latin for 'I think, therefore I am.'
From this breakthrough, he went on to prove that humans are dualist beings (spiritual minds inhabiting physical bodies). Descartes theorised that our bodies were like machines that would perish, and our minds where immortal, but never made it clear how the mind and body interact.
Descartes thought that God would guarantee abstract, rational thinking that was as 'clear and distinct' as the original 'Cognito' itself.
This means that our clear, mathematical thinking about the world is correct, but our sensory experiences of it are subjective and flawed. Descartes uses his scepticism to establish what sorts of certain knowledge there are.

	Created by Summer Pearce about 8 years ago

AS - Level (Year 1) Philosophy (4a) Traditional Arguments for the Existence of God - Onto.) Slide Set on The Ontological Argument, created by Summer Pearce on 10/03/2016.