Descartes' Critical Project: The Destruction of Knowledge

Philosophy 442/542
Fall 2010


In "Meditation One", Rene Descartes begins his search for knowledge---for knowledge that can withstand challenges and provide the solid foundation he sought for the sciences. It is interesting that a positive search for knowledge should begin here, though, since this meditation stands out as one of the most forceful expressions of epistemological skepticism ever produced. That is by design, however, since he is after knowledge that can withstand even this type of assault.


For Descartes, knowledge is justified true belief.

A. "Belief" is a relationship between us in virtue of a cognitive representation and the world.

B. "Truth", for our purposes, will be a property of claims when those claims describe the world the way it really is.

C. "Justification": for Descartes, as we'll see, this is absolute certainty---indubitability.

Meditation One: Skepticism, Cartesian Style

  1. Descartes' skepticism is "methodological skepticism"---he does not embrace it as a fact in the end. He uses it as a means to acquire knowledge.

    1. In fact, you can take the Meditations to be his attempt at applying the method he develops in the Discourse on Method to the foundations of the sciences. The skeptical work in the first Meditation is the analysis, and the synthesis is found in the remaining 5 meditations.

    2. Descartes' brand of skepticism is also called "epistemological skepticism," which is a deep and thoroughgoing rejection of the possibility of knowledge. (Focus on the principles and on his definition of knowledge.)

    3. His challenge is very important to the layman: if we cannot answer him, we may have to reconsider the standards we apply to our investigation of the world.

  2. GOAL: Descartes' primary goal in the Meditations was to establish a firm foundation for the sciences---to establish "firm and lasting knowledge."

    1. He believed this was impossible so long as one's belief system contained falsehoods.

    2. He was convinced that the only way he could achieve his goal would be to raze this structure and then rebuild it accepting only beliefs the truth of which he was certain---this was his way of getting JUSTIFICATION.

  3. METHOD: His was the SKEPTICAL METHOD---to reject as false any belief that could be doubted.

    1. Implication: that knowledge rests on indubitable belief---that with indubitability (and the absence of prejudice and blind faith in the senses) comes justification and truth.

    2. He applies this method to the foundational principles of his belief system and not to each belief individually.


    1. These derive from his target, Aristotelian science. (In a letter to his friend Mersenne, he confessed that the real goal of his Meditations was to refute Aristotelian science and replace it with his own.)

    2. For Aristotle, knowledge was ultimately grounded in sense experience; however, in addition, other faculties of the soul---the imagination and the intellect---were capable of contributing to one's store of beliefs.

    3. Therefore, Descartes focuses on 3 types of beliefs in applying his method: those that are sense-based (e.g., sitting by the fire), those that are imagination-based, and those that are based in the intellect. If he could cast doubt on these, the edifice of his beliefs would come crashing down.


    1. Against sense-based beliefs:

      1. Perceptual beliefs about distant objects: Illusion.

      2. Perceptual beliefs about proximate objects: Dreams.

    2. Against imagination-based beliefs:

      1. Example include those created in dreams.

      2. Composite beliefs such as these can be dismissed as dubitable, more or less on their face.

    3. Against intellect-based beliefs:

      1. These include mathematical beliefs of the kind that underpin arithmetic and geometry. (E.g., shape, extension, number, etc.)

      2. Deceiving God: Either there is a God or not; if so, then it is possible that he is a deceiver, and if he is a deceiver, then you could be wrong about what you consider most certain; if there is no God, then chance rules and we have even less reason to trust the dictates of our intellect.

  6. CONCLUSION: All beliefs that constitute his belief system are dubitable, and so are rejected as false. He is therefore mired in a deep skepticism. Keep in mind, though, that this is a philosophical skepticism and not a practical skepticism; nevertheless, he has to fight against erosion of his philosophical position brought on by the practical situation in which he finds himself.