I think, therefore I am?

"I think, therefore I am." Almost everyone has heard of this saying, but what does it mean?

It was coined by René Descartes, a famous mathematician, philosopher and scientist who lived in the 17th century. The phrase sums up one of the arguments he gave in his Meditations. If one truly opens one's mind to the possibility of what this argument is saying, it can lead to quite an altered state of mind, and a complete revision of this experience called 'reality'.  It is not unlike that feeling one has at the end of some movies where a piece of information is given which forces you to reevaluate every scene which came before.
 
Descartes is sitting comfortably by the fire. He decides to take on the challenge of discovering if there is anything that we humans can be absolutely certain of knowing. Can he be sure, for instance, that he is in fact sitting comfortable by the fire? He thinks that he could be having a dream.  So what can he be sure of?

Descartes begins his search by pretending that there is a demon who is continually inserting false beliefs into his head. So now, when he sees and feels the warmth of the fire, he can't be sure that the fire is there, as these sensations could have been thrown into his head by the demon. Descartes leaves his writing for a little in this skeptical frame of mind, being cautious not to be deceived by the demon. Everything that he sees, hears, touches, smells and tastes is no longer an indication of what is.

So when he returns to his writings, what does he find? He realises that the whole world might be an illusion created by the demon. Nothing around him, not even his own body, necessarily exists. But there is one thing that he can be sure of, and this is that he has thoughts. Therefore, his mind must exist! Otherwise, if the demon wanted to make him believe that he had no mind, he would have to insert that belief into his head, and he couldn't do this unless Descartes had one! Therefore, by logical necessity, if there is anything that he could be sure of, it is that if he thinks, he must exist. Hence the phrase: "I think, therefore I am."

However, this does not mean that we can be sure that other people exist - all we know is that "I", the thinker, exist.  It is very possible that every single other person which you perceive on a day-to-day basis does not, in fact, think, but only has the appearance of doing so.  What a frightening idea. You might like to try being suspicious of everything you see, hear or smell for the next few days, it really is a bizarre exercise. Of course, you don't have to believe in the demon, only the possibility that what you believe about this world may be a figment of your mind.


Further Reading:

• Descartes, R., Meditations on First Philosophy
• Bouwsma, O. K., 1949, "Descartes' Evil Genius", Philosophical Review 58, pp. 141 - 151