Descartes' Evil Demon Hypothesis:
The reason that things seem to you now the
way that they do is because there is an evil
demon deceiving you and manipulating your
mind at every second.
He is making you think about certain shapes
and colours and sights and sounds, even
though all of it is an elaborate trick, and none
of your sensations are verifiable.
So, even though it may seem to you now that
you are reading typed words on a screen, you
are really just being fed these sensations by
an Evil Demon, who doesn't want you to know
what the world is really like.
René Descartes (1596-1650)
In his ‘Meditations’,
Rene Descartes sets
out to determine,
what sorts of
things he
knows and
how he
knows them.
In order to determine this, he puts forward
the following two methods of doubt:
(i) He decided to examine
his foundational beliefs--e.g.,
whether he could trust his
sensory beliefs, mathematical
beliefs, etc.
(ii) If there is even the
slightest possibility of a
belief being false, he will
reject the belief as a
candidate for knowledge.
So, Descartes is
trying to determine what
sorts of things he
knows given that his
criteria for knowledge is
infallibility.
If there is any way that
he could be mistaken
about something, he
will discount it as
knowledge.
Descartes applies his method in the
following three ways:
1.The Senses Sometimes Deceive: Descartes reflects
on the fact that our senses sometimes deceive us.
When we are looking at something very small or far
away, for example, we can often be mistaken about
the size or shape of the thing in question. In addition
to these kinds of phenomena, there are also
hallucinations, optical illusions, and after-images. E.g.,
a straight stick might look bent when sticking
halfway out of water; and a red-orange after-image
can appear for awhile in your field of vision if you've
just stared at the sun too long.
Can you trust your senses?
Descartes admitted that even though
the senses can sometimes deceive in
these ways, they are usually pretty
reliable. So at this point he thought that
we should rule out knowledge through
our senses only when it came to things
that are very small or far away, or under
certain abnormal conditions. This still
leaves us with much that we do know
(e.g., that there is a screen in front of
you, that you have hands, etc.)
You Could Be Dreaming!:
2. Descartes next questions
whether we can distinguish
dreaming from being awake. For
example, in your dreams you are
usually quite convinced that you
are not dreaming. No matter how
crazy your dreams may be (e.g.,
you may fly or breath under water
in your dreams). So how,
Descartes asks, could you
possibly be able to determine
whether you are dreaming or
awake right now?
ARE YOU AWAKE????
Thus, since it is possible that you may be
dreaming right now, Descartes is going to
discount many of our beliefs as candidates for
knowledge. For example, you do not know
that there is a screen in front of you, you do not
know that you have hands, etc. For if you were
in fact dreaming right now, then none of these
things would be true. However, Descartes allows
that perhaps you still know about colours and
math and logic, since these will remain
unchanged whether you are dreaming or not.
THE EVIL DEMON
Lastly, Descartes
entertains the
possibility that he
is being deceived
by an evil demon.
This evil demon
could deceive him
into thinking just
about anything-e.g., that 2+2=4
even if in fact it
didn't; that red is a
particular colour
even if it weren't;
To illustrate: you can
imagine that every time you
try counting the sides of a
triangle, the evil demon
makes you think there are
only three sides when in fact
there are, say, four. All
Descartes really needs is that
the evil demon could get you
to do this once or twice, and
your foundation for
mathematical knowledge will
be destroyed.
For remember that
Descartes' criteria for
knowledge is
infallibility; so if you
are wrong about
something once, then
you could be wrong
again, and so you
cannot be counted as
knowing it.
I THINK THEREFORE I AM
Descartes concludes that
there is only one thing that he
knows for certain. This is his
famous cogito ego sum, which is
roughly translated as "I think,
therefore I am.“
For Descartes, a thinking thing is "a
thing that doubts, understands,
affirms, denies, is willing, is unwilling,
and also imagines and has sensory
perceptions." Since the demon would
have to deceive something in order to
carry out his deception, the deceived
must exist
The Cogito
“But what then am I? A thing that thinks. What is
that? A thing that doubts, understands, affirms,
denies, wills, refuses, and that also imagines
and senses … Is it not the very same ‘I’ who now
doubts almost everything, who nevertheless
understands something, who affirms that this
one thing is true, who denies other things, who
desires to know more, who wishes not to be
deceived, who imagines many things even
against my will, who also notices many things
that appear to come from the senses?”