Descartes distinguished between certainty and truth.
Certainty was a state of mind, but truth was an objective reality; certainty was a state of mind, but truth related to the way things actually are in the world.
Descartes was meeting a twofold problem. On the one hand, he had to deliver worthwhile conclusions and on the other hand he had to be able to defend his conclusions against the arguments of the skeptics.
He met these obstacles through a set of conditions.
He argued that you should not accept anything as truth that you could doubt.
He wrote,
Since I now wished to devote myself solely to the search for truth, I thought it necessary to . . . reject as if absolutely false everything in which one could imagine the least doubt, in order to see if I was left believing anything that was entirely dubitable.
On the face, Descartes recognized that he couldn't live in this manner. But Descartes attempted to get at the foundations of the sciences and at general truth about the world through this methodology of doubt.
He wanted to lay the foundations of inquiry, establishing a means whereby truth could be further pursued.
He endeavored to put the scientific enterprise into a shape where it could not be attacked by the skeptics (religious). He consequently engaged in preemptive efforts and said he would do all that the skeptics do and do it even better and as a consequence Descartes believed he would come out on the other side with a much greater confidence in knowledge and also with a greater argument advantage.
He seems he accomplished both objectives.
This led Descartes to the establishing of Cartesian Doubt as a method for determining certainty.
Again, Cartesian doubt worked by laying aside anything which he could doubt.
Someone has said that Descartes method in the method of doubt was like going through a barrel of apples, throwing out all of the bad apples and putting back only the good ones.
There were three stages to the development of the method of doubt.
First, Descartes spoke of laying aside ordinary common sense conclusions. For example, he cited the reality that sticks placed in water looked bent, which leads to the unreliability of the senses. This phenomenon proved that the senses could be misleading. But he wanted to go beyond these types of phenomena.
He penned,
I have found by experience that the senses sometimes deceive, and it is prudent never to trust completely those who have deceived us even once.
Second, he entertained the idea that he could doubt that we are awake and he posited the possibility that he was only dreaming. He drew from his own experience in this matter. In the past Descartes had experienced dreams which he thought was a conscious state but later he would awaken only to find that he was dreaming.
Descartes pondered even such seemingly straightforward judgments as "I am sitting here by the fire" as possibly being false since there was no guarantee that his present experience was not a dream.
How could he be certain that this wasn't happening at all times? How could he be certain that his perception of reality was not just a dream?
At the risk of over simplification, Descartes reasoned that if he were dreaming all of the time he would therefore have no concept of a dream. Consequently, his present state could not be a dream.
Finally, Descartes imagined, for the sake of the method, that an evil genie was deceiving him. He carried his doubt forward with this even more radical possibility of an evil genie which was "of the utmost power and cunning" who deceives him into thinking that everything, the sky, the earth and even all external things might be illusions that the demon has devised in order to trick him.
He imagined that if there were such an evil genie with this objective, was there anything which the evil genie could not mislead him about?
Ironically, this extreme consideration enabled him to devise the first indubitable truth in the Cartesian quest for knowledge, that is the existence of the thinking subject.
He concluded,
Let the demon deceive me as much as he may, he can never bring it about that I am nothing, so long as I think I am something . . . I am, I exist, is certain, as often as it is put forward by me or conceived in the mind.
Remember, Descartes meant this method as a tool or method, not for everyday living. With this method of doubt, Descartes endeavored to establish a sort of imaginative or intellectual critique.
Thus was born Cartesian Doubt.
