Descartes' Methodical Doubt and Certainty

Doubt and Certainty in Cartesian Philosophy

René Descartes is fully convinced of the capacities of reason and the usefulness of the rational method to find truth and true science. Descartes resolved to abandon doubt. Since he has admitted many false opinions as true, he will henceforth strive to reject as false everything in which he can imagine the slightest doubt. From this point of view, Cartesian doubt has some particular characteristics:

Methodical vs. Skeptical Doubt

First, it is a methodical doubt and not a skeptical doubt. Skeptics remain in their doubt and cannot find a way to overcome their uncertainties. Descartes, through this process, tries to reach the indubitable truth; thus, doubt is a means of getting at the truth.

Hyperbolic Doubt

Secondly, it is a hyperbolic doubt and not a natural doubt. Descartes exaggerates his doubt because the more rigorous and extreme it is, the more obvious and undeniable the truth that will be reached.

Criteria for Unquestionable Truths

Descartes used criteria to serve as a negative norm for truth, so that only realities capable of overcoming each of these criteria may be established as unquestionable truths. These criteria are:

• The Senses: They often deceive us; therefore, we cannot trust them.
• The Misuse of Reason: The arguments we believe to be rigorous and true can be misleading and false.
• No Distinction Between Sleep and Wakefulness: While we dream, things seem real, and only upon waking do we discover they were false.
• The Evil Genius Hypothesis: With the above reasons, the truths of mathematics are safe from doubt. However, to establish a universal and absolute doubt and take it to the end, Descartes turned to the evil genius hypothesis, thus subjecting even mathematical propositions to doubt. Descartes does not comply with them; he uses artificial reasons and asks us to suppose that there is a very powerful evil demon who deceives us constantly and prevents us from distinguishing any certain knowledge. In this case, we cannot accept anything as true.

The First Truism: Cogito, Ergo Sum

Amid this absolute uncertainty, the first truism shines forth: I doubt, therefore I must exist. If I doubt, I think, therefore I am.

The Foundation of Existence

We have, therefore, the first truism: I think, therefore I am (cogito, ergo sum). This proposition expresses its own reality. The very act of thinking, according to Descartes, provides the evidence of my existence; if I single out intellectual activity, this activity demonstrates my own existence.

The Criterion for All Truth

"I think, therefore I am" will not only be the first truth but will also serve as the criterion for all other truths—that is, the criterion that will distinguish the true from the false, success from error. It will also establish the scientific method that leads to the discovery of every other truth and the ideas that manifest this truth.