Rene Descartes penned one of the most famous phrases in the history of philosophy: “Cogito ergo sum,” or, “I think, therefore I exist.” This serves as a definitive means to establish absolute certainty, insofar as human beings may do so. The following will explain how Descartes arrived at this conclusion, by analyzing his “method of doubt” and clarifying the process leading to his assertion. Lastly, this paper will provide a brief explication as to why Descartes’s statement is important in epistemological terms.
In “Meditation I,” Descartes is seeking to build a clear foundation for a process in viewing belief and reality since, as he notes, many beliefs that he held in the past proved to be false. He proposes to achieve this by doubting everything that he perceives as subject to doubt, and adding true knowledge to his store of beliefs only when he has demonstrated that there is no reason to doubt it. To this end, he discusses that one of the primary sources of knowledge is the belief that our senses can be trusted. Descartes observes, however, that our senses sometimes deceive us. Dreams, for instance, seem real when we have them but are are not actually real; therefore, we can never be sure that the world is as it appears. For example, Descartes notes that having a paper in his hands and sitting by the fireplace may not be based on true sensations at all, but on the false sensations found in dreams that seem real. These sensations are then false because he is not actually reading a paper by a fire, but asleep. Following this line of logic, Descartes concludes that, since there is no clear way to distinguish life real life from dreams, any belief of reality based on sensation is inherently questionable (p.47 – 48). This reasoning, however, does not apply to arithmetic and geometry because it cannot be doubted that, whether we are awake or asleep, two plus three equals five, and a square has four sides (p. 49). This contrast in place, Descartes moves on to question God, another reality he views as absolute, and one going to the certainty of what he has determined is certain . More exactly, he wonders whether God makes him believe that earth, heaven, and the realities of science are real, when in fact they might not exist at all.
This same doubt of the reality seen as most evident is taken further by Descartes. He supposes that, instead of God, there is an evil force with supreme powers that puts all his energy into deceiving him. This would mean that all of Descartes’s beliefs, from trust in heaven to the reality of the material world, are illusions of reality (p. 50). Descartes consequently concludes that it is not in his power to obtain true knowledge; therefore, all he may do is avoid false beliefs. Proceeding from this conclusion, Descartes proposes in “Meditation II” that we possess no actual senses; our bodies and physical perceptions are all illusions in our mind, as we cannot with certainty know what they are. This leads to Descartes’s single and powerful conclusion. If any idea of reality may be false, and this knowledge means we cannot be certain of any, it nonetheless follows that there remains the reality of the “I.” No matter the illusion, there must be an “I” that is convinced, and an “I’ that exists because it undergoes this process of belief. Consequently, an actual basis or beginning for epistemology is created, for Descartes’s statement means that there can be actual knowledge. The importance to epistemology is hard to overstate, if only by virtue of the intense process of “distilling” Descartes uses to arrive at his truth. “Cogito ergo sum” may provide only a single basis of confirmed knowledge, but it is nonetheless a standard by which all other investigation of knowledge and reality may be done. As one principle of knowledge is irrefutable, it is then possible to assess the certainty of all others, and there can be no epistemology without this core.