Apart from the sufferings of middle school students with the Cartesian plane in geometry, Descartes is best known for his “method of doubt.” He wanted to know if there was anything of which he could be certain, so he resolved to doubt anything he could.
The history of France? No, he’d only read and heard what others said about it. The existence of the world? No, he might be dreaming or deceived by an evil demon. The existence of his own body? Same problem. It seemed that there was nothing of which he could be completely certain.
Except for one thing: His mind existed, because if he could doubt that his mind existed, then he had to have a mind with which to doubt it. Whatever else might be doubted, he existed as a thinking being. He could know that for sure.
Cogito, ergo sum! he cried, and leapt to his feet, alarming the other patrons of the tavern in which he’d spent the evening.
“Cogito, ergo sum” means “I think, therefore I am.”
Tragedy almost struck later that evening when the tavern was about to close. The bartender asked, “Would you like another drink, Mr. Descartes?” Descartes pondered for a moment and then replied, “I think not.” Poof! He disappeared in a puff of logic. Luckily for us, he reappeared a moment later, laughing. It was one of his favorite party tricks.
But this blog post is about Thomas Reid. To prevent misunderstandings, I should mention that he was related neither to John Reid (the Lone Ranger), Britt Reid (the Green Hornet, also the grand-nephew of the Lone Ranger), nor to Tara Reid (the actress, no relation to any of the other Reids). Thomas Reid’s ideas must stand or fall on their own.
Descartes’ argument “I think, therefore I am” is usually considered a pretty good one, but Reid would have none of it.
Reid argued that certain assumptions were necessary for any thought at all. As a result, you couldn’t prove them without circular reasoning because in order to prove them, you first had to assume that they were true.
According to Reid, it was completely nuts to reject such assumptions even though they could never be proven. And here’s where we get to his juicy critique of Descartes. It’s a marvelous piece of writing:
“A man that disbelieves his own existence is surely as unfit to be reasoned with as a man who believes he is made of glass. There may be disorders in the human frame that may produce such extravagances, but they will never be cured by reasoning.”
And Reid himself doubts that Descartes was really serious:
“Descartes indeed would make us believe that he got out of this delerium by his logical argument Cogito, ergo sum. But it is evident he was in his senses all the time, and never seriously doubted his existence. He takes it for granted in his argument, and proves nothing at all. I am thinking, says he, therefore I am: And is it not as good reasoning to say, I am sleeping, therefore I am? Or I am doing nothing, therefore I am?”
Common sense has always been in short supply, especially in philosophy. If Reid’s brand of clarity appeals to you, give him a read. It’s well worth your time.