“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)
