Absolute Certainty and the Cartesian Circle
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.
But this veridical guarantee gives rise to a serious problem within the Meditations, stemming from the claim that all clear and distinct ideas are ultimately guaranteed by God’s existence, which is not established until the Third Meditation. This means that those truths reached in the Second Meditation, such as “I exist” and “I am a thinking thing,” and those principles used in the Third Meditation to conclude that God exists, are not clearly and distinctly understood, and so they cannot be absolutely certain. Hence, since the premises of the argument for God’s existence are not absolutely certain, the conclusion that God exists cannot be certain either. This is what is known as the “Cartesian Circle,” because Descartes’ reasoning seems to go in a circle in that he needs God’s existence for the absolute certainty of the earlier truths and yet he needs the absolute certainty of these earlier truths to demonstrate God’s existence with absolute certainty.
Descartes’ response to this concern is found in the Second Replies. There he argues that God’s veridical guarantee only pertains to the recollection of arguments and not the immediate awaRenéss of an argument’s clarity and distinctness currently under consideration. Hence, those truths reached before the demonstration of God’s existence are clear and distinct when they are being attended to but cannot be relied upon as absolutely certain when those arguments are recalled later on. But once God’s existence has been demonstrated, the recollection of the clear and distinct perception of the premises is sufficient for absolutely certain and, therefore, perfect knowledge of its conclusion (see also the Fifth Meditation at AT VII 69-70: CSM II XXX).