Published online by Cambridge University Press: 05 December 2011
Valid arguments – even those with true premises – do not take you very far if you do not know whether the premises are true. The fact that I am in Heidelberg does not give me a reason to believe I am in Germany unless I know (or at least have reason to believe) I am in Heidelberg. So why does everyone believe the Cogito – I think, therefore I am – is such a terrific argument? Because, I suppose, everyone thinks he knows the premise is true. Everyone who thinks he thinks thinks he knows he thinks. So everyone thinks his existence – at least his existence as a thinking being – is the conclusion of an irresistible argument.
The Cartesian inference is certainly valid, no doubt about that. And the premise is clearly true – at least it is for everyone who thinks it is true. I am not questioning either of these claims. I do, however, think it worth pondering the question of whether – and if so, how – one knows that the premise is true. What reason do thinkers have for thinking they think? If you are going to demonstrate, à la Descartes, that you exist, you need a premise you know to be true. Merely thinking you think is not good enough to generate knowledge you exist anymore than (merely) thinking you are in Heidelberg can generate knowledge that you are in Germany. As my title is intended to suggest, the most it will generate is a belief – perhaps (depending on whether you have any reasons for thinking you think) an altogether groundless belief – that you exist. In epistemology you cannot manufacture A+ conclusions from C- premises. Garbage in, garbage out.