What can we know? Lisa lines up the thoughts of one of the world’s biggest thinkers to explain how little we really know… By Lisa McLellan
Today I will introduce you to Descartes and one of the most well known statements in modern philosophy,
Descartes is widely considered the father of modern western philosophy. His writings and his methods set the stage for the development of philosophy and his topics of discussion are still hotly debated today.
The baby and the bathwater…
Descartes put forward cogito ergo sum (I think therefore I am) in his Meditations. His aim in the Meditations is to establish a foundation on which to build a body of sure and certain knowledge. He begins by doubting everything which he previously accepted as true. In this way, he razes his current body of knowledge, eliminating any false presumptions. This sets the stage for a firm foundation of knowledge to be established.
Can we trust our senses?
Descartes first doubts the information he receives from his senses. He considers that his senses often deceive him, leading him to believe something which on closer inspection turns out to be false. He therefore concludes that information from the senses must be rejected as uncertain and unreliable.
He then questions whether it can be doubted that he is in his chair, by the fire, wearing his winter dressing gown. He considers that he often dreams when he is sleeping, and dreams often lead us to believe that we are somewhere we are not. He can find no definite rule by which to distinguish between dreams and reality, and so he is forced to admit the possibility that he may be dreaming. He therefore must reject such beliefs, eg. his belief that he is sitting in his chair, as uncertain.
Even if he were dreaming, Descartes realises that certain truths would still hold. The truths of mathematics and geometry, for example. Even in sleep, two plus two equals four, and a triangle always has three sides. Can these truths be doubted?
Descartes finally pulls out his ace. He asks himself whether he can be sure that God is not deceiving him into believing falsehoods. If this were possible, he would have grounds to doubt even mathematical truths. Of course, concludes Descartes, God is all good and would never do such a thing.
Might there not, however, be a powerful demon who is deceiving Descartes?
Descartes concludes that this is indeed possible, and so it seems that he must reject all his prior beliefs.
It seems that Descartes is left with nothing. After further deliberation, however, Descartes finds one remaining truth of which he can be certain. He realises that he must exist in order to be deceived. What one can be sure of is that if one is deceived, then one exists. The mere act of doubting, believing or thinking presupposes existence. I think, therefore I am.
Descartes takes this as his foundation of knowledge. Is he right?
It may be argued that even the statement ‘I think, therefore I am’ is open to doubt. Just because there is a thought, must there be a thinker? Just because there is doubt, must there be an ‘I’ who doubts?