Absolute Certainty and the Cartesian Circle

by the IEP

Recall that in the First Meditation Descartes supposed that an evil demon was deceiving him. So as long as this supposition remains in place, there is no hope of gaining any absolutely certain knowledge. But he was able to demonstrate God’s existence from intuitively grasped premises, thereby providing, a glimmer of hope of extricating himself from the evil demon scenario. The next step is to demonstrate that God cannot be a deceiver. At the beginning of the Fourth Meditation, Descartes claims that the will to deceive is “undoubtedly evidence of malice or weakness” so as to be an imperfection. But, since God has all perfections and no imperfections, it follows that God cannot be a deceiver. For to conceive of God with the will to deceive would be to conceive him to be both having no imperfections and having one imperfection, which is impossible; it would be like trying to conceive of a mountain without a valley. This conclusion, in addition to God’s existence, provides the absolutely certain foundation Descartes was seeking from the outset of the Meditations. It is absolutely certain because both conclusions (namely that God exists and that God cannot be a deceiver) have themselves been demonstrated from immediately grasped and absolutely certain intuitive truths.

This means that God cannot be the cause of human error, since he did not create humans with a faculty for generating them, nor could God create some being, like an evil demon, who is bent on deception. Rather, humans are the cause of their own errors when they do not use their faculty of judgment correctly. Second, God’s non-deceiving nature also serves to guarantee the truth of all clear and distinct ideas. So God would be a deceiver, if there were a clear and distinct idea that was false, since the mind cannot help but believe them to be true. Hence, clear and distinct ideas must be true on pain of contradiction. This also implies that knowledge of God’s existence is required for having any absolutely certain knowledge. Accordingly, atheists, who are ignorant of God’s existence, cannot have absolutely certain knowledge of any kind, including scientific knowledge.