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Epistemology: Descartes
Epistemology: Descartes
Revision Booklet
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Epistemology: Descartes
Area 1:
Searching for a reliable foundation of knowledge
Meditation 1
Descartes’ aim: finding a foundation of certain knowledge
From an early age Descartes was convinced that problems existed in the generally accepted
theories of knowledge. These problems had led to serious errors in scientific enquiry, eg the
belief that the Sun revolved around the Earth. The problems appeared to lie in questionable
foundations. If something is wrong with the foundations of a house then any builder will
tell you that the house will soon have major problems.
Descartes’ aim was to establish a foundation for knowledge that couldn’t lead to mistakes .
Without this foundation, Descartes believed it would be impossible to establish something
that is ‘firm and lasting in the sciences’.
Descartes’ method (Cartesian doubt)
In order to find certainty in science and in fact all disciplines, Descartes realised that he
must ‘raze everything to the ground and begin again from the original foundations’. To do
this he realised that he couldn’t assume that any of his beliefs were tr ue. He must begin by
assuming that all his beliefs were false and then only adopt those that he could say were
beyond doubt.
Descartes’ sceptical method of doubt, then, has two basic requirements:
1.
rigour – Descartes’ sceptical method demands that he mus t ensure that there is not
the slightest degree of doubt about anything that can be called knowledge
2.
a shortcut – by focusing on foundational beliefs, Descartes can show clearly and
quickly which beliefs should be dropped and which could be called knowle dge).
Rejection of a posteriori knowledge claims
Optical illusions
Descartes began his search by considering the widely accepted Aristotelian reliance on
sense experience as the key foundation of knowledge.
Whatever I had admitted until now as most tr ue I took in either from the senses or
through the senses.
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Descartes immediately noted that there had been times when his senses had deceived him.
His rigorous method demanded that:
it is a mark of prudence never to trust wholly in those who have deceive d us even once.
So, should all knowledge based on sense experience be rejected? Descartes quickly pointed
out that it is only a particular type of sense experience that appears to regularly cause error,
eg when observing very small and distant things. So maybe it is only this type of sense
experience that should be thrown out.
However Descartes quickly goes on to suggest two reasons for beginning to question the
certainty of even these simple sense experiences.
First, he suggests that it’s quite possible that he’s mad. The insane, after all, are not aware
of their madness.
The dream hypothesis
Descartes’ second worry is intensified by the realisation that when he is dreaming, his grasp
of what is real is no more certain at that moment than if he were awake and insane. Is it
possible that he is currently ‘sleeping between the blankets’? Is it possible that his
experience of the sheet of paper and the dressing gown is not real, that it is just a dream? Is
it possible that everything that his senses confirm to him is, in fact, simply part of a dream?
Descartes cannot present a strong argument that will prove that he is asleep and dreaming.
However, for the sake of argument he suggested that it is a possibility. Descartes was
looking for certainty. He was looking for a foundation that could not be disputed. He must,
therefore, allow this unlikely but still possible scenario. By presenting the dream argument
Descartes was suggesting to his readers that sense experience can easily be doubted. If this
is the case then the senses, the most common foundation of our knowledge claims, should
not be called a foundation at all. Descartes’ radical suggestion that he may be dreaming is a
deliberate attempt to undermine the Aristotelian emphasis on sense experience.
Knowledge that survives the dream argument
Descartes’ first point is simply that an outside world must exist. He based his argument on
the thought that there must be something on which our dreams are based. The painter
observes the physical world and draws a representation of what he sees onto canvas. In a
similar way our dreams are a representation of the reality of a physical world. If there were
no physical world then the painter would have nothing to paint and we would have nothing
to dream about.
Secondly, even if you are fast asleep, the truths preserved in mathematics cannot be
doubted. A square does not have more than four sides and 2 + 3 still equals 5. The dream
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argument can’t really challenge these simple mathematical truths. They are true whether I
you are awake or fast asleep.
Descartes has come to these two conclusions using his mind alone. He has not needed to
make reference to his senses to show us that even if he’s dreaming there must exist an
outside world and mathematical truths are still certain. Although the dream argument
appears to have destroyed reliance on a posteriori truths, it has not destroyed reliance on a
priori truths.
Rejection of a priori knowledge claims
The Evil Genius hypothesis
Is it possible to doubt even necessary truths? Immediately after his discussion about
dreaming Descartes’ mentions that there is one belief that he has had confidence in
throughout his life. He is sure that God exists. Descartes’ method demanded that he
questioned what he had previously known. Maybe, he says, God brought it about that there
is no earth at all, no heavens, no extended thing. Maybe I am “deceived every time I add
two and three or count the sides of a square”. However, Descartes did not just believe in
God, he also had strong beliefs about God. A significant belief that he held was that God is
supremely good. This should make it clear that God would not deceive him into thinking
that there is a world outside his mind or that God would deliberately make him think that 2
+ 3 = 5 is a necessary truth when in fact it is not. He decided, though, that i n order to find
the certainty that he was searching for he must carefully withhold his assent from all things,
not just those things that are obviously false. Descartes actively chose to consider even the
most unlikely of possibilities.
Descartes did not just believe that God was good, he was also taught from childhood that
God was omnipotent (all powerful) and omniscient (all knowing). If God has these two
attributes but is evil instead of good then suddenly even a priori truths are open to doubt. If
God is an evil deceiver then he could will at any time to make us think that we are grasping
with our minds a necessary a priori truth when in fact we are not. Certainty now seems to
be an almost impossible task. Even the things that survived the dream argumen t (the
apparently certain a priori truth that there is an outside world and the certainties of
mathematics) can now also be doubted. Maybe the images in human dreams have been put
there by the deceiver? Likewise 2 + 3 appears to equal 5. But what if the de ceiver is
constantly tricking us about the meaning of these symbols? What if the deceiver is
constantly tricking us about the logical processes involved in any mathematical equation?
Descartes was aware that the chance of there actually being an evil dec eiver is not high. He
was presenting the evil deceiver as another hypothesis. Now, after the introduction of this
extreme hypothetical radical doubt, Descartes had to accept that even a priori truths could
not be his desired foundation. In fact, if there i s a deceiver then nothing is certain.
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Diabolic Doubt
Descartes began his second Meditation with a statement of what has been called diabolic
doubt. Now nothing was certain. There appeared to be no foundation that could give him
the certainty that he desired. The sceptics appeared to have won.
By the end of Meditation 1 Descartes had managed to undermine Aristotle’s sense -based
tradition and Plato’s reason-based tradition. He had at the same time subtly questioned all
the traditional avenues for certainty that dominated Medieval scholastic philosophy:
1.
2.
3.
4.
authority
sense experience
reason
God.
In fact, in his short first Meditation Descartes had essentially undermined the whole of
Western philosophy
Summary: Meditation 1
 Descartes’ aim was to find certain knowledge.
 The method of doubt demands that every belief must be scrutinised rigorously.
 To make his task possible, Descartes focused his attent ion on previously cherished
foundations of knowledge.
 The dream argument challenges all a posteriori knowledge claims.
 A priori truths such as 2 + 3 = 5 survive the dream argument.
 The evil genius hypothesis challenges everything, particularly a priori knowledge
claims.
 The extreme doubts expressed in Meditation 1 appear to have undermined 2500 years of
Western philosophy.
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Area 2:
Reason is the foundation of knowledge
Meditation 2: the cogito
In order to establish something firm and lasting i n the sciences, Descartes had chosen to
push scepticism to its limits. He had chosen to present the most extreme argument available
to him, by presenting the possibility that God is an evil deceiver. He presented this extreme
argument in order to find out if he could defeat it. If he could find something that survived
the evil genius then he certainly found something firm and lasting.
At this point that Descartes identified something that at last he calls certain knowledge.
Then there is no doubt that I exist, if he the deceiver deceives me. And deceive me as he
will, he can never bring it about that I am nothing so long as I shall think that I am
something.
Descartes’ foundation of knowledge is the simple observation that he was consc ious of the
fact that he exists. It’s not just that Descartes proved theoretically that he existed. Descartes
knew that he existed.
Can you explain in detail why the cogito is a foundational, self-authenticating
knowledge claim?
The phrase ‘I am: I exist’ is often described as a necessary truth. It led Descartes on to
reflect in some depth about the nature of the ‘I’. Descartes still insisted on the hypothetical
possibility of an evil deceiver so he could not ‘know’ anything about his physical body. All
he could know was that he was thinking.
The cogito is Descartes’ first principle of philosophy. It appears beyond dispute because it
is a self-authenticating statement. It is clearly self-contradictory to say ‘I don’t exist’.
‘self-evident’ statements defeated the infinite regress argument because to ask for further
justification is a meaningless exercise. For example, it is ridiculous to ask, ‘How do you
know that a cat is a feline creature?’ In the same way, it is clearly ‘self -evident’ that ‘I am:
I exist’ is a self-evident truth or that ‘thinking requires a thinker’. Descartes presented his
readers with the ultimate infinite regress argument which culminates with the question
‘How do you know that you are not being deceived by a n evil deceiver?’. He then cleverly
used the most powerful question any sceptic could ever ask as the very trigger for his own
certain foundation of knowledge. Descartes ended the infinite regress by finding a truth that
is beyond dispute.
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Descartes’ belief that he existed, a belief which is absolutely ‘certain and assured’, would
be the foundation for his ‘firm and permanent structure in the sciences’. The key point here
for Descartes is that his foundation was found through the process of ‘thinking alon e’.
Descartes hadn’t based his foundation on sense experience. For Descartes, the cogito
showed that reason must take priority over experience. He tried (possibly successfully?) to
show that a priori truths are more certain that a posteriori truths. For Descartes, there was
clearly something special about ‘thinking’.
Why is the cogito an argument for rationalism?
Descartes’ reflections on the nature of ‘man’ all end up coming back to the mind. For
Descartes, the central mark of a human is that he/she is a conscious, thinking thing. These
reflections in Meditation 2 are all part of Descartes’ desire to replace Aristotle’s sense based philosophy with his rationalistic agenda. ‘I am: I exist’ survived the evil genius.
Descartes’ conscious mind alone allowed him to overcome the most sceptical of arguments.
For Descartes, then, rationalism and not empiricism should be the foundation of knowledge.
The senses were easily defeated. Reason, although appearing initially to succumb also to
the genius, survived in the end.
In an earlier text, the Discourse on Method (1637) Descartes had made a similar point. In it
he used a phrase that has become possibly the most memorable phrase in philosophy:
Cogito ergo sum (I think, therefore I am)
Summary: Meditation 2
 The cogito has been used to defeat the most extreme sceptical arguments.
 The statement of diabolic doubt at the beginning of Meditation 2 has been overcome.
 The cogito has provided the key foundation for Descartes’ future knowledge claims.
 ‘I am: I exist’ is a unique example of a self-authenticating, necessary truth.
 ‘I am: I exist’ is the starting point of Descartes’ argument that reason should take
priority over empiricism.
 The cogito has defined something unique about the nature of what it is to be human.
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Meditation 3 (God as guarantor of clear and distinct perceptions)
Can you explain in detail what Descartes means by clear and distinct perceptions?
Descartes has proved that he exists. However, in order for this to be a useful foundation he
needed to be able to build something on it.
In order to proceed further in his search for knowledge Descartes spent some time analysing
the cogito in order to identify what was special about it. Why can he know with certainty
that he exists and is a thinking thing but he doesn’t know with certainty that physical
bodies exist? The answer is that the cogito has a distinguishing feature. What makes the
cogito certain is that Descartes claimed to have a ‘clear and distinct’ perception of it. It is
logically possible to doubt the existence of physical bodies, but logically impossible to
doubt his own existence as a thinking thing. Descartes then argued that whatever els e he
understood clearly and distinctly must also be true.
When Descartes talked about ‘perception’ he did not mean sensory perception. ‘Perception’
was Descartes’ term for what the mind does when it becomes aware of simple truths. In
other words, it is when we ‘see things’ with our mind’s eye.
In the Meditations he gave other examples of clear and distinct perceptions. For example,
he had a clear and distinct idea that ‘I exist, insofar as I am a certain thinking thing’, or that
‘what is done cannot be undone’. There are perceptions that Descartes said we cannot think
about without at the same time knowing they must be true.
Clear and distinct ideas are essentially knowledge that can be grasped by intuition. This is
knowledge that can be understood by intellect or can by the illuminating light of reason. An
intuition is a truth that is known a priori. Knowledge that is clear and distinct is knowledge
acquired just by thinking without any reference to experience. They are self -justifying and
self-evident truths upon which Descartes hoped to build ‘something firm and lasting in the
sciences’.
 Clear = present to the attentive mind
 Distinct = not confused with anything that is not clear
What is the clear and distinct rule?
The clear and distinct rule becomes a kind of test, a truth-rule, that should be used to help
find other pieces of certain knowledge. Descartes wished to say that the most important
mark of any knowledge claim is that it must be founded on a clear and distinct perception.
If the cogito can be considered Descartes’ foundation of knowledge, the clear and distinct
rule is going to be the thing that allowed him to build upon this foundation.
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But still, before Descartes could move on he reminded his readers that in the past the evil
deceiver had made him doubt these earlier clear and distinct perceptions. In order for
Descartes to establish this new truth-rule and be able to build on his certain foundation he
must first attempt to remove the evil deceiver from his own mind, and ours.
Can you explain Descartes’ Trademark argument for the existence of God?
Descartes’ strategy was to prove that a perfect God exists. Given that perfection includes
goodness rather than deception, this is not a God that would deliberately deceive you.
Descartes could not just say that God might exist, or that it’s highly likely that God exists.
Rather, he must be able to say with certainty that God must exist. As you might expect,
Descartes’ strategy for proving the existence of God would be one that was d one using the
mind alone. He wanted to find out whether he could know God exists a priori.
Descartes’ argument, although appearing confusing when first read, is really quite
straightforward. It can be summarised in a variety of ways. Here is one possible
interpretation:
Step 1
When Descartes looks into his mind he sees that he has an idea of a perfect being. At the
same time he knows that he is imperfect. The logic here is that Descartes believes that in
order for humans to understand our own imperfect ion, we must first have an idea of a
perfect being.
Descartes believes that this is true for all humans. All of us recognise our imperfection only
because we understand perfection.
Step 2
Descartes believes that it is self-evident that nothing will come from nothing. In other
words, the idea of a perfect being must have a cause. So, where did the idea of perfection
come from? What is its cause?
Step 3
The causal principle states that the cause of something must be sufficient to produce its
effect. So, an imperfect mind is clearly not sufficient to produce the idea of perfection.
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Step 4
I can’t be the cause of this idea of perfection because I am imperfect. So there must exist a
perfect being, who placed this idea in my mind. This perfect being has left his/her
trademark in my mind.
Descartes argued that the only possible explanation for why he understood the idea of
perfection was because God has left his mark in his mind. And, given that perfection cannot
include deception, this God must be good. Also, this perfect being must be all powerful
(omnipotent) and all knowing (omniscient) so, therefore, able to control the evil deceiver (if
there is one, which he has already suggested is not likely!).
The proof is completely carried out in Descartes’ mind. It is, therefore, a priori in nature.
For Descartes, this proof of God is a significant example of a clear and distinct perception.
Summary: Meditation 3
 The defining feature of the cogito is that it is clear and distinct in Descartes’ mind.
 Descartes believes that anything that is clear and distinct can also then be called
knowledge.
 Something is clear and distinct if it is certain beyond doubt, based on an intuition of the
mind and is a self-evident truth.
 Mathematical certainties are further examples of clear and distinct perceptions.
 Descartes believes that he has a clear and distinct perception of a perfect being.
 The only possible explanation for the idea of perfectio n is that the perfect being must
have left his trademark on us.
 God is essential to any possibility of knowledge beyond the cogito.
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Area 3:
Meditations 6: Refuting the sceptical arguments
How does Descartes overcome the sceptical doubt that he cannot know whether there is
an outside world?
Descartes’ strategy to show that he could know with certainty that the material world is a
reality relies on the clear and distinct rule and his proof t hat God exists and is good.
Commonsense tells us that the source of our sensations of the world around us must surely
originate in the physical objects themselves. But could Descartes successfully prove this
simple piece of common sense knowledge?
“It remains for me to examine whether material things exist.”
Descartes’ argument can be split into two simple steps. The argument is based around the
simple sensation that we all have of the world around us. The sensations of the world
outside his mind can only possibly originate from either his own mind, from the actual
outside world or from God choosing to put these sensations into our mind.
Step 1: The sensations we have of materials things come from outside the mind.
First Descartes wishes to make clear that the sensations he has in his mind of materials
things do not originate from within his own mind. To justify his conclusion he presents two
simple arguments.
First of all he points out simply that these sensations are not subject to his will. He cannot
control their appearance or their smell. His mind then cannot have willed these sensations.
They must, therefore, have come from outside his mind.
Second, he points out that his sensations of material things give h im the idea that they are
extended things. In other words they appear to represent things which have size and shape.
His mind, however, is unextended, it has no size or shape. Descartes argues that an
unextended thing (the mind) cannot create or cause the idea of an extended thing. Therefore
the sensations that we have of material things must come from outside his mind.
Step 2: The sensations we have of materials things must originate in physical matter itself.
If the sensations that we have of material t hings don’t originate in our minds, where do they
come from? There are, according to Descartes, only two possibilities. Either they come
from the material world itself or they come from God. Descartes simply points out that he
has a strong inclination to believe that there is a physical world. He has already shown that
God must exist and that this God must be good (perfection cannot include any idea of
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deception). Therefore, God would not give us ideas about an outside world if it wasn’t in
fact true. God is no deceiver; therefore the sensations of the physical world could not come
from God. The only possibility left is that they must originate in the material objects
themselves.
How does Descartes overcome the sceptical argument that we can never have knowledge
based on our senses?
Descartes was determined not only to show that the material world exists, but also that our
senses can in fact be trusted to provide knowledge of what it is like.
How does Descartes achieve this?
Reason should have priority over the senses
First of all he makes the case for giving reason priority over the senses. He does this by
proposing that the mind has two distinct parts, the imagination and the intellect. The
imagination is the part of our mind that visualises the material things. The intellect is the
part of our mind that understands the material things. To explain the distinction Descartes
uses the example of a chiliagon. First he asks us to imagine a triangle, visualise it in your
mind. This, hopefully, you should be able to do. He then asks us to imagine a chiliagon.
Can you visualise in your mind a 1000 -sided figure?! Descartes then points out that we can
understand ‘clearly and distinctly’ what a chiliagon is whereas we cannot properly visualise
it using our imagination. This allows us, Descartes suggests, to conclude that the
imagination is a distinct faculty from the intellect.
Descartes goes on to discuss in detail these two distinct faculties of the mind by suggesting
that our minds perceive the world in two s pecific ways.
The imagination
The imagination allows us to perceive, what John Locke would later call the secondary
qualities of matter. These are qualities such as sounds, smells, colours, textures etc.
Descartes argues that these qualities can only be perceived in an obscure and confused
fashion.
Descartes argues also that the physical matter perceived through the imaginatio n is simply a
sensation of the way matter appears to our particular perceiving minds. For example,
matter itself is not actually coloured, rather there is something else within the particular
object that causes us to perceive colours.
The intellect
The intellect is the part of the mind that allows us to perceive the primary qualities of
matter. These are qualities such as mass, shape, quantity etc. Descartes suggests that these
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qualities can be understood clearly and distinctly. This allows Descartes to argue that these
primary qualities 1 are inherent features of the objects. His justification for this conclusion
is that God would not allow us to be deceived about what we clearly and distinctly perceive
about these objects. They must, therefore, be a part of the essence of the object itself.
Should we trust our sensations of the outside world?
Descartes again argues that God would not deceive us and so we should be able to
confidently say that the sensations we have of the outside world via the senses are a good
representation of how the world actually is. However, we must not be lazy when we
interpret the world via our sense experience. He remains adamant that our senses do often
deceive us. However, he wishes to make clear that, with a careful use of reason, we are in
fact able to have knowledge of these material objects. We know how they appear in our
imagination. We can then check this sensation with our clear and distinct understanding of
the object’s primary qualities. Our senses do at times lead us to make mistakes about the
world. However, with a careful use of reason, we can recognise and correct the errors in
sense perception.
Descartes’ argument can be summarised as follows:
1.
2.
3.
4.
5.
Our intellect should take priority over our imagination.
The intellect can understand the primary qualities of objects clearly and distinctly.
God is no deceiver and so we can have knowledge of the primary qualities of objects.
If we can have knowledge of the primary qualities of objects, we can therefore have
knowledge of the essence of the objects.
God is no deceiver and so we can trust our senses to give us a go od representation of
the secondary qualities of the objects.
Conclusion: With a careful use of our God-given reason, errors in sense perception can be
recognised and corrected.
Overcoming the dream argument
Descartes presented the dream argument as the final nail in the coffin of reliance on the old
Aristotelian idea that sense experience is the foundation of our knowledge claims. The
dream argument didn’t get rid of our knowledge of the material world, or th e truths
available in mathematics. However, it did leave us unable to trust our sense experience of
even the simplest things. Descartes ended his Meditations with some simple observations
designed to show how to distinguish between a waking and a dreaming state.
He presented two ways of working out whether or not you are awake at any given moment:
It is important to emphasise that Descartes doesn’t use the terms primary and secondary qualities himself
anywhere in the Meditations. These were terms used later extensively by the empiricist John Locke. However,
Descartes’ discussion of the different qualities of matter does reflect the meaning that Locke gave to these
terms.
1
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1.
All normal life follows a coherent pattern of actions. These patterns are clearly
recognised in our memory. Dreams, on the other hand, are all over the plac e! If at one
moment you are enjoying listening to your philosophy teacher waffle on about the dream
argument and then you suddenly find yourself having an argument with your mum in the
kitchen then you can be sure that you are in fact dreaming. If the phil osophy class takes a
steady but slow 55 minutes and then you get up and head off to the next subject on your
timetable then you can be sure that you are awake.
2.
Strange things can happen when you are asleep! If you find yourself floating over
the school watching your friend working, then it’s likely that you’re asleep. If the laws of
cause and effect are working normally then you can be sure that you are awake.
Reason can again be used to show whether or not you’re awake or dreaming. God also isn’t
likely to allow us to be deceived into thinking that we’re fast asleep. If we can know that
we’re not dreaming then we can know that our sense experiences of simple realities are
trustworthy.
Summary: Meditation 6
 Descartes wants to refute the sceptical arguments so that he can show that reason should
take priority over sense experience.
 Descartes wants to be able to say with certainty that he can know things beyond his own
mind.
 His mind is unextended whereas he has perceptions of an extended world. This suggests
to Descartes that his mind cannot then be the source of his sensations of the outside
world.
 God cannot be the source of these perceptions either, because God would not deceive
him therefore the material world itself must exist.
 Descartes suggests that he can trust his sense perceptions because God would not
deceive us. Because God is no deceiver the representations we have in our minds of the
world can be trusted.
 Our clear and distinct perceptions of the qualities of objects such as their size , location
etc allows us to say that with a careful use of reason we can correct errors in our sense
perceptions.
 Descartes knows he cannot be dreaming because waking life follows a linear pattern of
experiences that runs within the bounds of the rules of cause and effect.
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Area 4: Evaluation of Descartes’ Meditations
Evaluation of Descartes’ method
Was Descartes’ sincere?
Descartes’ method encourages the use of hyperbolic doubt. In other words, he intends to
reject beliefs if he has any grounds whatsoever for being suspicious of their truth. Some
have challenged the sincerity of Descartes’ method. Could it be that the doubts he raises are
just a sham, and that Descartes had a pretty good idea of what he wanted to prove from the
outset? Maybe Descartes has presented some pretty serious doubts but in reality didn’t take
them seriously himself? For his method to be effective then Descartes needed to genuinely
destroy all his opinions. It could be argued that he only ever pretended to doubt key belief s
like his conviction that God exists.
Was Descartes consistently rigorous?
Descartes’ method of doubt demands a rigorous approach. It can certainly be argued that Descartes
was indeed very rigorous early in his Meditations. Maybe we should give him the benefit of the doubt
and accept his sincerity. However, maybe he wasn’t quite so rigorous when he later tried to build
upon his foundation. Maybe his building work was a little lacklustre. The criticisms that follow could
certainly be used to back up this opinion.
Was Descartes too quick dismissing empiricism? (Problems with his Dream argument)
Descartes suggests that he regularly mistakenly takes the experience of dreaming for
reality. In other words he seems to be saying that when we are asleep we have no way of
distinguishing sleep from reality. Most can understand these comments as most of us have
experienced the sensation of waking up and for a moment or two not been quite sure
whether or not we are still dreaming. However, it doesn’t take long for us t o realise that we
are in fact awake. It does appear true that we mistake dreaming experience for conscious
experience when we are asleep and dreaming. However, do we necessarily make the same
mistake when we are awake?
When we’re asleep we can’t clearly distinguish wakefulness from sleep. However, when we
are awake we do seem to be able to check fairly easily. For example, when we dream our
sense of touch doesn’t appear strong. Rather, dreams are very visual. Dreams also do not
have the continuity of waking experience. They tend to be dominated by brief episodes that
often contain strange occurrences. Descartes himself presented arguments in Meditation 6
to show that with a careful use of reason he could distinguish wheth er or not he was
dreaming.
It has been argued then that Descartes seems to have made a logical error in Meditation 1.
He takes the apparently true proposition:
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When I’m dreaming I regularly mistakenly assume that this experience is real.
And then moves to the apparently false proposition:
I cannot ever tell the difference between dreaming experience and conscious experience.
This means that his conclusion that he can’t tell whether or not he is asleep now isn’t
necessarily the case. If he’s dreaming now he has a problem. However, if he’s awake now
then he can know this experience is true.
Descartes presented the dream hypothesis as a final nail in the coffin of reliance on sense
experience. A priori truths survived it but a posteriori truths didn’t. Descartes was
therefore using the dream argument to begin his case for the superiority of rationalism as
opposed to empiricism. If we can challenge Descartes’ presentation of the dream argument
then maybe his argument against empiricism isn’t quite as strong as he had hoped.
However, some may argue in response that Descartes doesn’t really need to worry too much
about any problems with the dream argument. After all, the evil deceiver argument,
although initially raised to challenge a priori truths, clearly could also be used to challenge
a posteriori truths. The point Descartes is really going to make is that only his mind can
overcome radical doubts like the dream argument or most importantly the evil genius. Even
if the criticisms above are true they don’t really affect the principle that he is trying to
establish.
Does Descartes’ method of doubt lead to a sceptical dead-end?
The addition of the evil deceiver is certainly the most rigorous of all arguments. However,
this rigour led the famous Scottish philosopher David Hume to argue in his Enquiries
concerning Human Understanding (1748) that once hyperbolic doubt is embarked upo n
then nothing can survive. Theoretically all our beliefs can be doubted. Descartes’ method,
therefore, according to Hume, leads to a sceptical dead end.
The question for us to ask is whether or not Descartes was successful in escaping the diabolic doubt
he presents us with.
Summary: Evaluation of Descartes’ method of doubt
 Were Descartes’ doubts sincere?
 Was he rigorous throughout the Meditations?
 Did he make a logical error with his dream argument?
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 Does his method lead to a sceptical dead-end?
 Did his method change the way scientists and philosophers approached their work?
 Does his method of doubt challenge us to be more careful about our beliefs?
 Is his search for certainty a realistic and necessary goal?
Evaluation of the cogito
Many of the criticisms directed against the cogito are based around Descartes’ references to
the evil deceiver.
The evil deceiver and reason
The cogito was Descartes’ first key foundation of knowledge. It is clear that it can only be
called certain knowledge if we agree that logic itself is reliable. However, the evil deceiver
hypothesis means that we must doubt even the reliability of logic itself.
P1
P2
C
If I’m thinking then I must exist.
I am thinking.
I must exist.
Although on the face of it the cogito does appear self-evidently true, there are clearly
logical steps involved in Descartes’ argument. If there is an evil deceiver, then maybe we
have to accept that some of these steps could be false. For example, maybe it’s logically
possible that thinking doesn’t in fact need a thinker! Maybe the deceiver has tricked us into
making this premise seem self-evident! If the reliability of reason is doubted then how can
Descartes hope to use reason to overcome his doubts?
However, unlike the classic argument, ‘I think therefore I am’, it could be argued that the
version of the cogito expressed in the Meditations, ‘I am: I
exist’ is immune to this criticism. ‘I am: I exist’ is not an argument, rather it is meant to be
understood as an undeniable self-evident proposition. There are no logical steps here for the
demon to undermine. There is no hidden premise like ‘thoughts require a thinker’. Rather,
‘I am: I exist’ is presented by Descartes as a statement that you can know is true as soon as
you express it.
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The evil deceiver and language
The doubts raised by the evil deceiver were designed to throw into doubt not just all a
posteriori knowledge but significantly all a priori knowledge claims. After the possibility
of us being deceived by the evil deceiver, even simple mathematical concepts like 2 + 3 = 5
are open to doubt. Descartes’ cogito is supposed to be the self-evident truth that survives
even the demon hypothesis. However, in order for the cogito to work it could be argued that
Descartes must have had at his disposal a list of fundamental language concepts. Descartes
must have known what ‘thought’ is, what ‘doubt’ is, w hat ‘existence’ is, what ‘I’ is etc,
before he was able to put together these ideas into the cogito. If we can’t be sure of the
meaning of these concepts, then maybe we can’t be sure that ‘I am: I exist’ is a necessary
concept after all.
Problems with Descartes’ assumption about the meaning of the word “I”
Here is a short collection of some of these responses. 2 All of them relate to Descartes’
assumptions about the nature of the ‘I’ referred to in the cogito.
David Hume (1711–1776) had earlier raised an objection to Descartes’ idea of the ‘self’.
He argued that when he thought most intimately about what he called his self he only ever
experienced ‘some particular perception or other, heat or cold, light or shade, love or
hatred, pain or pleasure. I never can catch myself at any time without a perception, and can
never observe anything but the perception.’ For Hume, experience and not reason should be
the foundation of knowledge claims. Hume concludes that the concept of ‘self’
merely refers to a bundle of perceptions. There is no independent self in which these
perceptions occur. All we can know is that experiences of perceptions are happening.
Georg Lichtenberg (1742–1799), the eighteenth-century German physicist, also questioned
Descartes’ basic assumption about what the ‘I’ in the cogito is. Lichtenberg argued that to
say ‘I think’ contains more than we can be certain of. He argued that the most we can say
is, ‘It thinks’.
Bertrand Russell (1872–1970) argued that Descartes’ foundation of knowledge i ncludes a
large assumption about what the ‘I’ actually is. Descartes believed that the ‘I’ is a ‘thinking
thing’ which led him to the conclusion that the mind (where the ‘I’ is housed) is distinct
from the body. Russell’s criticism is designed to point out that this fundamental idea is
based on a less than secure assumption. He points out that when we look at a table we can’t
say for sure ‘I am seeing a brown table’. The best we can say with certainty is ‘a brown
colour is being seen’. For Russell, all that can be proved is the existence of the momentary
perceptions.
A.J. Ayer (1910–1989) argued that Descartes was wrong to use the words ‘I think’. If he was to be
really consistent with his sceptical approach then the most he should have said was ‘there are
2
Cardinal, Hayward and Jones (2006), pp 55–60.
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thoughts’. Descartes was making the assumption that if there are thoughts then there must be a
thinker, however, maybe the evil deceiver hypothesis can challenge even this simple idea.
Summary: Evaluation of the cogito
 Could the deceiver trick us into believing that it is self -evident that thoughts require a
thinker?
 Could the deceiver trick us about the meaning of our language concepts?
 Is Descartes right to assume that a human is primarily a thinking thing?
 Maybe all Descartes can say with 100% certainty is that ‘there are thoughts’ or ‘it
thinks’?
Evaluation of Descartes’ reliance on God
The role God plays in the Meditations has already been emphasised. If God can’t be shown
to exist then Descartes can’t really get beyond the cogito. He may have established the truth
that he exists. However, without God this is pretty much all he’s achieved. Many today
aren’t nearly as convinced of the existence of God as Descartes was.
Problems with the Trademark argument
Maybe innate ideas don’t exist?
The trademark argument relies on our innate idea of God, perfection etc. However, maybe
innate ideas don’t exist in the first place? Maybe Descartes’ understanding of God isn’t an
innate idea, maybe it’s simply something his mind has invented to suit his purposes. Many
people also have different ideas about what God is. For example, not everyone agrees that
God needs to be all powerful. If the idea of God is innate, why is it that there is often so
much disagreement about what God actually is like?
Problems with the causal adequacy principle
Maybe this principle isn’t in fact true? Is it possible to find examples in the world that
challenge this assumption? Look at the following two examples: 3
We light a bonfire with a match.
We can cause an avalanche with a whisper.
3
Cardinal, Hayward and Jones (2006), p. 100.
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Here the cause appears to have less reality than what was produced.
The effects of a long process such as evolution could also be cited. Tiny, apparently
insignificant changes taking place over a huge length of time can lead to the development
of disorganised matter into complex life forms. The final effect is clearly much greater than
the original causes.
Maybe God chooses to deceive us for his own mysterious purpose?
Descartes has assumed that God wouldn’t deceive us because deception is a flaw that a
perfect being could not have. However, maybe God has perfect reasons for choosing to
deceive us?!
Maybe the evil deceiver is deceiving us about our idea that God wouldn’t
deceive us (that God is good, perfect etc.)
If we take seriously Descartes’ radical doubt then why should we not apply it to all our
common understanding of the nature of God? Maybe the evil deceiver deceives us into
thinking that God wouldn’t deceive us? Maybe the evil deceiver put the idea of ‘perfection’
in our minds?
If the trademark argument is open to doubt then Descartes has not achieved his fou ndation
of knowledge.
If we are successful in casting doubt on the existence of God and his nature then Descartes’
reliance on reason should also be rejected. If the deceiver is a real possibility then I should
give up the belief in argument itself as a means of acquiring the truth. The remainder of the
Meditations is full of various arguments, eg existence of God, clear and distinct rule,
mind/body duality etc. If we honestly need to take seriously the possibility of the existence
of an evil deceiver then we need to honestly accept that Descartes’ arguments may all be
open to doubt. They can only work if a good God exists. The question remains though, has
Descartes successfully argued that God must exist?
Summary: Evaluation of Descartes’ reliance on God
 Has God been defined into existence?
 Can we be certain that there are innate ideas?
 Can we find counter-examples to challenge the causal adequacy principle?
 Maybe God chooses to deceive us for his own good purposes.
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 Maybe the evil deceiver put the idea of perfection into our heads.
 If God doesn’t exist then all Descartes knows is that he exists.
Evaluation of the clear and distinct rule
Is Descartes’ rule ‘invalid’?
Descartes argued that the success of the cogito was down to the fact that it can be grasped
clearly and distinctly. He then generalised this principle and claimed that any belief he can
conceive clearly and distinctly must also be true. A simple criticism can be levelled at
Descartes here by asking whether or not this is a valid g eneralisation. If someone observed
one pink pig and then generalised that all pigs were pink we would be justified in assuming
that this generalisation is unacceptable. 4 Maybe Descartes’ generalisation with regard to the
clear and distinct rule is equally invalid.
How can we know for sure whether something is clear and distinct?
Another obvious difficulty concerns our ability to recognise whether a belief we have is
actually clear and distinct. It is surely possible to think that you’ve identified something
clearly and distinctly when in fact you haven’t. Descartes isn’t clear on how you can
guarantee that you have indeed come to a clear and distinct knowledge claim. In Meditatio1
he took a great deal of time to show us how easy it is to be mistaken when making a
knowledge claim. Surely then it’s possible to mistakenly call something clear and distinct
when in fact it is not. Descartes, after all, made it clear on more t han one occasion that he
considered man to be ‘subject to error’.
The Cartesian circle
In order to help guarantee that we can in fact have knowledge based on the clear and
distinct rule, Descartes needs to make reference to God. His argument is simple:
P1
P2
C
God exists and is good.
A good God would not deceive us into thinking that something is clear and distinct
when it is not.
We can therefore trust our intuition about what beliefs are in fact clear and distinct.
This argument leads us into what is often presented as the most significant criticism of the
Meditations. Descartes appears to use circular logic.
4
Cardinal, Hayward and Jones (2006), p. 83.
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We have already noted the difficulties that can be directed at the Meditations due to the
role played by God. According to Descartes there are certain truths that are so clear, so
self-evident that we simply know them to be true and one such truth concerns the existence
of God. The problem for Descartes is that he needs God to establish the reliability of
reason. To know that God exists in the first place he needs to know that his mind is
reliable. This argument was first raised by a contemporary of Descartes, a theologian called
Antoine Arnauld. Although he was one of the first to adopt the philosophy of Descartes, he
did so after outlining this key reservation.
Descartes’ argument does appear to be circular, ie it presupposes what it sets out to prove.
To prove that his clear and distinct judgements must be true he needs to rely on God. To
know that God exists he needs to rely on the clear and distinct ideas required in both his
trademark and his ontological proofs.
Q
A
Q
A
How do you know that God exists?
Because I proved his existence using clear and distinct ideas.
How do you know that clear and distinct ideas are reliable?
Because a non-deceiving God exists.
God exists
These enable
me to know
that
Clear and
God’s existence
means that the
following are
reliable
distinct ideas
Summary: Evaluation of the clear and distinct rule
 Is this rule invalid?
 How can we be sure that something is a clear and distinct perception?
 Does Descartes use circular logic?
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Glossary
Key term
Definition
Cartesian
The adjective from ‘Descartes’. Used to describe
philosophical and other ideas related to Descartes.
Cartesian circle
The name given to a particular objection to
Descartes’ argument. Descartes needs the notion of
clear and distinct perception to move beyond the
cogito but needs God to guarantee the reliability of
clear and distinct perception.
Cartesian doubt
The sceptical method used by Descartes in which any
belief that is not certain is treated as false
Causal adequacy
principle
The principle that the cause of an object must
contain at least as much reality as the object itself.
Clear and distinct
perception
In the Principles Descartes says that a ‘clear’
perception is one that is present and manifest to the
attentive mind and that a ‘distinct’ perception is one
that is so separated from all other perceptions that it
contains absolutely nothing except what is clear.
Cogito
Latin for ‘I think’. Used as a way of referring to
Descartes’ argument that he cannot doubt his own
existence
Evil genius
A hypothetical entity used by Descartes to maintain
the possibility that we are constantly being deceived.
Method of doubt
Descartes’ attempt to arrive at certainty by
systematically doubting everything until he
discovered something that could not be doubted.
Trademark argument
Descartes’ argument that God must exist because we
have an idea of God and the idea must have been
implanted there by God as a kind of trademark.
Tick box
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Examples of Exam Questions (Higher)
KU / AE
YEAR
1.
What role does the evil genius play in Descartes’
method of doubt?
10KU
2007
2.
Explain why Descartes later believes that he can be
confident that physical objects exist.
8AE
2007
3.
Is Descartes successful in his attempt to rebuild
knowledge?
12AE
2007
4.
Why does Descartes believe the statement “I am, I
exist” to be “necessarily true”?
10KU
2008
5.
Does the statement “I am, I exist” provide a certain
foundation for knowledge?
20AE
2008
6.
Why did Descartes write the Meditations?
4KU
2009
7.
Explain the role God plays in Descartes’ argument.
6KU/4AE
2009
8.
How far has Descartes achieved his aims by the end
of Meditation Three?
Give three examples of what Descartes might regard
as clear and distinct perceptions
16AE
2009
3KU
2010
What does Descartes mean by seeing something
3KU
“clearly and distinctly”?
Explain how Descartes employs the idea of clear and 8AE
distinct perceptions in his attempt to establish certain
knowledge.
What problems are there with Descartes’ use of the
6AE
clear and distinct rule?
2010
13.
What evidence is there in the Meditations that
4KU/6AE
Descartes is a rationalist? Give examples to illustrate
your answer
2010
14.
Describe the arguments Descartes uses to arrive at
a position of universal doubt in Meditation One.
10KU
2011
15.
How effective are Descartes’ sceptical arguments in
Meditation One?
6AE
2011
16.
Critically evaluate the claim that the cogito is beyond
doubt
5KU/9AE
2011
9.
10.
11.
12.
2010
2010
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