For the class in Modern Philosophy I'm taking this semester, we have to write 15 two-paged papers (minimum) on philosophers such as Descartes, Hume, Locke, and Leibnitz. In this essay, I wrote about Descartes' Meditations (fifth and sixth). The following is my submission:
In his fifth and sixth meditations, Descartes seeks to apply his epistemological framework to questions relating to the existence of material objects, the contingency of knowledge upon the existence of God, erroneous judgments which originate from sensation, and the various differences between mind and body.
Among that which Descartes perceived as true included mathematics. Descartes wrote that various theorems he had formerly intuited as true were, in fact, necessarily true, not due to his limited imagination, but because the nature of that to which the theorems pertain imposed upon his mind their eternality and immutability. A corollary Descartes constructed yielded a second argument for the existence of God: viz. Descartes could not conceive of a non-existent God because existence is a perfection, a truth imposed onto his mind. God’s essence – a perfect being – must therefore entail His existence and, as such, must exist. Since Descartes’ epistemological foundation is essentially grounded in the concept that God mediates this and all other knowledge to His creation, Descartes observed that all knowledge – including mathematical – is dependent upon God’s existence.
Because a perfect – omnipotent – God exists, Descartes claimed to know that, if nothing else, material objects possibly exist. But as Descartes believed that “all that we clearly and distinctly perceive is true,” in order to adequately justify the actual existence of material objects, he also believed that one must first examine ideas in one’s own consciousness in order to discover which are clear and which are confused. The imagination, writes Descartes, is the special exertion of the cognitive faculty whereby one contemplates some object. Because he claimed to be unaware of a means of contemplation of an object aside from sensation, Descartes asserted that the objects themselves probably exist materially.
Descartes then proceeds to reflect on whether or not the existence of material objects can be known with certainty. Reviewing his former reasons for accepting their existence, he explains that the vividness of sensation impressed upon him the idea that he could not have produced such thoughts and that he could not account for the seeming correlation between his body and feelings (e.g. hunger and stomach pains). But when he considered that he could simply be dreaming, could be deceived, or could even possess a subconscious sixth sense such that these imaginations were factitious, Descartes came to doubt the reliability of sensation. Upon constructing his philosophy, however, Descartes began to reexamine the validity of acquiring knowledge by sensation, and he claimed that God – who is by definition not deceptive – would indeed be deceptive if external objects did not exist, as Descartes claimed to clearly perceive that material objects exist. Moreover, as he was able to clearly differentiate one thing from another, although he knew he possessed a body, he also knew he was, in essence, simply a thinking thing. Still, he claimed that the conjoined nature of the mind-body relation is such that he should not doubt that there is some truth in the various perceived correlations between the mind and body. These are things Descartes claimed to be taught “by nature,” or by impulsive reactions to sensations for the purposes of self-preservation. Due to the finiteness of man and misuse of free will, however, these stimuli can actually hinder self-preservation, for upon further consideration the mind may understand that to follow the inclination is hasty or dangerous.
The question with which Descartes wrestles is: given His existence, why doesn’t a perfect God stop this? In order to answer this question, Descartes briefly compares and contrasts the mind and body. The mind – which is indivisible or unanalyzable – receives impressions from the body – which is divisible – via sensation. God could stop us from feeling pain et. al. by stopping certain sensations, but Descartes notes self-preservation would be hindered, as one wouldn’t know what could harm his person. Descartes observed, however, that the senses are more often reliable than not, and that his memory, understanding, and all other faculties are, when in agreement, able to discover the causes of judgment errors as well as means of prevention: because God does not deceive, what is clear is true, and what can, after careful consideration, be doubted should not be regarded as knowledge. This is Descartes’ epistemic criterion for knowledge.
The primary problem with Descartes’ reasoning is that his epistemic criterion is predicated on his own, fallible thoughts. He writes, for instance:
“I frequently considered many things to be true and certain which other reasons afterward constrained me to reckon as wholly false…will it be that I formerly deemed things to be true and certain which I afterward discovered to be false? But I had no clear and distinct knowledge of any of those things, and, being as yet ignorant of the rule by which I am assured of the truth of a judgment, I was led to give my assent to them on grounds which I afterward discovered were less strong than at the time I imagined them to be.”
If the only way Descartes can know that his perception is not clear is by a modus tollens argument – that is, “because this perception was wrong, I did not actually perceive with clarity” – then he has no grounds upon which to be assured that at some future point in time he will not perceive that his past perceptions were unclear. At best, he can know that his clear perceptions are possibly contradictory, which undermines his entire position.