“Cogito, ergo sum” (I think, therefore I am)
French philosopher and mathematician, Rene Descartes is often called the father of modern philosophy. Known to physicists as the discoverer of the law of refraction in optics, but Descartes’s most famous work is in philosophy. Meditations of First Philosophy set the agenda for speculation in the philosophy of mind and epistemology for at least the next 300 years. He raised problems of such radical scepticism about our knowledge of the world that he suggests the only thing one can be absolutely certain of is the fact of one’s own existence, an insight summed up in his famous edict “cogito, ergo sum,” popularly translated as “I think, therefore I am.”
Descartes’ program in the Meditations is to put the edifice of human knowledge upon secure foundations. Reviewing his beliefs, he finds that many are contrary. Some are more or less justified than others; some, such as the propositions of mathematics, seem certain; others readily turn out to be false. He resolves to put some kind of order into this jumble of beliefs so that justification from one proposition may follow from another. In order to do that he needs to begin with whatever is most certain and infallible. The question is, where to start?
Descartes comes up with an ingenious program. Rather than attempt to examine and order each belief in turn – as task impossible to contemplate – he decides to examine his beliefs against a method of doubt. The method of doubt consists in questioning the source of his beliefs and asking whether that source is infallible. If not, he can be sure that any belief from that source cannot be relied upon to provide the foundations of knowledge.
To begin with, Descartes notes that many of his beliefs are derived from his senses, or from perception. He notes that the senses, however, can often mislead. A stick may look bent when viewed half submerged in water, the true size of the sun and the moon is many times greater than would appear from sight, and so on. One can even suffer hallucinations such that what one thinks to be there does not exist at all. Descartes resolves not to trust completely that which has deceived him once, and therefore rejects any information from the senses as being uncertain and fallible.
Even so, one might think that although the senses may deceive from time to time, Descartes can be sure, at least, that he is sitting in his study, or is a Frenchman with an interest in philosophy and so on. Be he recognizes that there is no clear and distinct way of telling the difference between reality and dreaming. How does he know that the life he thinks he is leading is not just part of a dream? There are no clear ways of distinguishing between waking life and a life merely dreamt.
So, rejecting all perceptual knowledge, Descartes turns to what he believes on account of his own internal reflections. Surely he knows that 2 + 3 = 5, that a mother is older than her daughter, that a triangle has three sides? But it could be the case, reflects Descartes, that he is the subject of a massive deception. Now Descartes imagines a scenario wherein he might be deceived by a divinely powerful, but malignant being; a demonic being that could manipulate his thoughts, as God might if he were not supremely good, into thinking anything the demon might choose.
This idea of wholesale radical deception has been the subject of popular films such as The Matrix and Twelve Monkeys. Descartes realises, however, that there is one proposition that neither the evil demon nor even God could make false. This is that at any time when he thinks, it must be the case that he exists. For he must exist in order to be able to think. By such reasoning Descartes is led to the cogito as the one certain, infallible rock of knowledge.
For Descartes, the cogito was the beginning of a project in which he attempted to prove the existence of God, in order to guarantee the rest of human knowledge. His commentators, unimpressed by his weak version of Anslem’s ontological argument or his own “trademark argument” to prove the existence of God, have taken the Meditations to be the definitive work of epistemological scepticism.
[Summarized from Philosophy 100 Essential Thinkers by Philip Stokes, 2012.]
Lord, Give Us Today Our Daily Idea(s)