Archimedes used to demand just one firm and immovable point in order to shift the entire earth; so I too can hope for great things if I manage to find just one thing, however slight, this is certain and unshakeable. (Med, 16)
At this point in the Second Meditation of Descartes' Meditations on First Philosophy, the meditator finds herself in "a deep whirlpool," (Med, 16) where perhaps the only thing that is certain is that there is no certainty. Having trained herself to consider anything that could admit the slightest doubt as utterly false, the mediator searches for her Archimedean point, an undeniably certain datum that, once found, will act as the balance upon which the certainty of all subsequent knowledge can be measured. Offered informally as the famous cogito reasoning in the Second Mediation, this logical argument is used by Descartes to posit the meditator's knowledge of the existence of "I," or self as a thinking substance, as the unshakeable datum:
- Thought, as an act, inheres in a substance.
- I am thinking.
- Therefore, I exist at least as a thinking substance.
Although this argument is valid, it is not sound in the context of the method of doubt; the first premise presupposes concepts of thought and substance, the veracity of the second premise relies similarly on the preconceived notion of thought, and the second premise depends on, at the very least, the thinnest interpretation of "I" to be found in the conclusion, while also implying the preconceived notion of consciousness.
The First Premise: Presupposing Substance
The cogito reasoning is not a sound logical argument because its first premise, that thoughts, as acts, inhere in a substance, presupposes concepts of thought and substance. At this juncture in the doubt, the meditator has acknowledged that she knows nothing, but her progress is betrayed when Descartes allows the preconceived notion that acts require the agency of substances without any support for his claim. When this assumption is later challenged, Descartes explains that he holds as self-evident that "no act or accident can exist without a substance for it to belong to" (Reply to Hobbes). As demonstrated by his words concerning Euclid's Elements, Descartes again proves that it is the arrogant nature of the mathematician to treat fundamental proofs as axiomatic truths, and as a mathematician, Descartes is no exception to the rule. Additionally, the current state of the doubt describes an empty universe, but the first premise of the cogito argument presupposes the existence of acts and substances; even in an empty universe, there can be no room for this conceptual premise. Although Descartes' cogito reasoning can be reconstructed as a valid logical argument, his presupposition of concepts of thought and substance in the first premise of the argument leaves the cogito unsound.
The Second Premise: The Nature of Thought
The weakness of the cogito argument is found again in the second premise because its veracity depends entirely on the preconceived notion of thought, an unallowable dependency in context of the Method with respect to the Second Meditation. If the presupposition of the relation between thought and substance in the first premise is allowed, is the meditator correct in claiming that the persistent thoughts somehow belong to or are happening inside of her, making her the host substance proper to the act of thought? Unfortunately, Descartes leaves this question unanswered, failing to give a method for identifying the source of thought. Instead, he dismisses this essential identification as something known "without affirmation or denial" (Letter to Clerselier), appealing again to the preconceived notion of thought by claiming that the association of thought with its agent is an inherent function of the act of thought itself. Although at first Descartes seems to successfully extend his method of doubt to all knowledge, after observing his repeated appeal to preconceived notions of thought, it is clear that Descartes' Method is not sufficiently thorough, and his cogito argument suffers the consequences.
Lichtenberg's Challenge: The Problem of "I"
Even when considering the thinnest interpretation of the "I" to be found in the conclusion, the cogito argument is still found to be weak because the second premise implies the preconceived notion of consciousness, and it must be considered whether or not disjoint acts of thought can be construed as a unified entity. In his challenge to the cogito reasoning, German thinker Georg Lichtenberg argues that the meditator can only conclude "thought is happening," not "I am thinking" (Hatfield, 103). This challenge seems to be deflected when one considers the thin interpretation of the "I" of the conclusion: the second premise, "I am thinking," can be read as "I am the act of thinking," and Lichtenberg's challenge becomes merely an echo of the premise he is criticizing. By equating "I" with the thought episode, the meditator can argue soundly that whenever a thought episode occurs, so occurs the "I."
However, the concept of the thought episode connotes duration; it is not an instantaneous incident, and Descartes does not support the claim that individual thoughts in apparent succession form one contiguous event. Notwithstanding the lack of support for this conceptual leap, the unified "I" is attributed to the preconceived notion of consciousness. Concerning the preconceived notion of consciousness, Descartes does not show that disjoint, instantaneous thoughts could not create between themselves an ethereal notion of consciousness, whose nature as a notion is to engender further notions of unity, or "I." Lichtenberg's challenge returns, and the cogito argument remains unsound.
Conclusion
Descartes' cogito reasoning can be reconstructed as a valid logical argument; however, in the context of the Method insofar as it has progressed by the Second Meditation, the argument is not sound. The premises presuppose concepts of thought, substance, and consciousness, and even when the thinnest interpretation of "I" to be found in the conclusion is considered when evaluating the second premise, the premise nevertheless depends on the preconceived notion of consciousness, a condition Descartes attempts unsuccessfully to dismiss by again involving preconceived notions of thought.
