In Meditation VI, René Descartes attempts to complete his epistemological project by proving the existence of a material world. After the radical doubt of M1 and the foundations laid in M2 to M5, such as the certainty of the cogito and the existence of a non-deceiving God, Descartes now turns to an argument that combines God with observations of the nature of sensory experience. He first examines the nature of imagination, then evaluates sensory experience, considers our sources of error, and finally, through the clear and distinct rule and God’s truthfulness, concludes that material things must indeed exist.
Descartes begins by observing that he possesses the faculty of imagination, noting that it is different from pure understanding. He defines imagination through the example of geometry: “When I imagine a triangle, for example, I do not merely understand that it is a figure bounded by three lines, but at the same time I also see the three lines with my mind’s eye as if they were present before me.” (7:72) In contrast, when he thinks of a chiliagon, he can understand it but cannot imagine it with any clarity. This distinction shows that imagination requires “a peculiar effort of mind which is not required for understanding.” Since imagination depends on something beyond pure thought, it would not be an essential property of the mind, as he could not conceive of himself existing without it. Yet he recognizes that “if I lacked it, I should undoubtedly remain the same individual as I now am.” (7:73) Therefore, imagination “depends on something distinct from myself.” Descartes infers that the exercise of imagination may arise from the mind’s “application to a body which is intimately present to it,” (7:72) suggesting that the existence of imagination points to the existence of a body. Although Descartes achieves only a speculation of the existence of materials things at this stage, as he can conceive imagination as arising from some internal faculty rather than an external object, this line of reasoning establishes a foundation of the corporeal.
Descartes subsequently turns to the way sensory experience presents the existence of external objects. He recalls that before engaging in the meditating, he took it as “not unreasonable for me to think that the items which I was perceiving through the senses were things quite distinct from my thought,” this is because sensory ideas impose themselves on the mind “quite without my consent,” (7:75) appearing more vivid and lively than the ideas he forms voluntarily in thought. The involuntary nature of sense perception leads him to believe that these perceptions “came from other things.” Yet Descartes quickly makes a concession. He notes that sensory judgments are prone to error: regarding external senses, distant towers appear round but are square up close, the dream argument makes people mistake reality; regarding internal senses, amputees feel pain in phantom limbs. Here, Descartes appeals to the radical doubt, questioning his former claim that sensations correspond to an external reality rather than to mere mental illusions.
Thus, on top of these two arguments, Descartes invokes the existence and nature of God. Having proven in M3 that God exists and is no deceiver, Descartes mentions a crucial principle: “I know that everything which I clearly and distinctly understand is capable of being created by God so as to correspond exactly with my understanding of it.” (7:78) From this principle, he infers that if he has a clear and distinct idea of something as distinct from another, God can indeed make them distinct in reality. Applying the C&D rule to the distinction between mind and body, Descartes observes: “I have a clear and distinct idea of myself, in so far as I am simply a thinking, non-extended thing; and on the other hand, I have a distinct idea of body, in so far as this is simply an extended, non-thinking thing.” (7:78) Therefore, he concludes, “it is certain that I am really distinct from my body, and can exist without it.” This clarifies that the idea of corporeal substance is coherent and could correspond to something that truly exists.
Descartes moves forward to claim that since sensory ideas occur “without my consent” and “I could not avoid having sensory awareness of them when they were present,” he clearly and distinctly does so. Descartes rejects the possibility of false sense-perceptions because it would make God a deceiver, if He were to have him believe falsely that sensations come from external objects when they do not. Thus, since God is no deceiver, and since God has given Descartes a strong natural inclination to believe that sensory ideas come from bodies, it follows that material things truly exist: “God would not have given me this inclination without providing some means of knowing that it is true.” (7:79)
In short, the mind’s clear and distinct idea of body, combined with the fact that sensory perceptions appear to come involuntarily from outside, leads to Descartes’ conclusion that there must be an external, material world whose reality corresponds to these perceptions.
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