Glossary of terms (plus objections) for Descartes’ Meditations
Meditation I
Epistemology
The theory of knowledge – what it is and how we can secure it
Scepticism
The idea that no knowledge is secure and that doubt is inevitable. In Descartes’ time
people were sceptical about religious knowledge and scientific knowledge.
Methodological scepticism
To combat the sceptics, Descartes used their own method: doubting everything he
could to try and discover knowledge which was secure.
Foundationalism
The idea that knowledge must rest on a secure foundation. Mathematical knowledge
is an example: it rests on axioms (self-evident, intuitively true propositions) and
discovers new knowledge by employing self-evidently true operations (such as the
Law of Equality where if you have an equation, adding (or subtracting etc.) anything
to one side as well as the other maintains equality). Foundationalists hold that all
knowledge must be like this.
Rationalism
The position that claims knowledge is primarily gained through thought.
Empiricism
The position that claims that knowledge is primarily gained through our senses.
Descartes thought this position wrong (he is a rationalist) arguing that our senses are
not totally reliable and so cannot deliver reliable knowledge.
Sense-experience/sense-datum
A particular piece of knowledge delivered by the senses e.g. the red pen, the taste of
coffee.
Dreaming Argument
Descartes’ puts an empiricist objection: surely I can know my own body exists? Well
no, he answers, in dreams I appear to myself to be experiencing a ‘physical world’ but
we know that there is not really such a physical world in dreams – so it is possible that
I am now dreaming the ‘real waking world’ In that case, he lets the empiricist reply,
even if the physical world does not really exist, that I am dreaming it exists, the fact
that my ‘dream’ is crowded with objects implies (in the philosophical sense) that such
objects must also exist somewhere outside my mind. Descartes replies that we cannot
be so sure: in our dreams we concoct “sirens and satyrs” i.e. objects which are false.
Finally, the empiricist can say that the sirens and satyrs are composed of components
which cannot have been made up by my mind (the ‘Simples’), so implying they exist
outside it.
Descartes’ Simples
The basic components which seem to be impossible to synthesise in the mind –
including colour, extension, shape, mass, size, number, time.
Evil Demon Argument
His final strike against the empiricist and, indeed, against those thinking mathematical
knowledge secure: even the ‘Simples’ might be false knowledge being fed into the
mind by an evil demon (or ‘malign spirit’) together with a sense of certainty. Even
though in dreams “2 + 3 = 5 and a quadrilateral figure has no more than 4 sides” the
demon could vary these ‘truths’.
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Psychological Certainty
He points out that certainty is not the same as truth. Mad people (who “claim to be
kings”, “have an earthenware head”, “are made of glass”) are certain that they know
‘truths’ which we know to be false.
Objections
To foundationalism:
 He gives no explanation or justification for the claim that all knowledge must
be foundational in character. Scientific knowledge is as secure as we could
wish but we know it is not foundational: it is based on theories which, by their
nature, are provisional.
 It is incoherent to jettison all beliefs as he recommends (like emptying all the
apples from a basket and then replacing the sound ones). We need some
beliefs to allow us to judge other beliefs – they can’t all be jettisoned.
To his rejection of empirical knowledge
 False empirical knowledge is capable of being corrected (as Descartes himself
says when he relates how a distant tower appears round but, closer to, turns
out to be square) by ‘better’ empirical knowledge. The ‘counterfeit coins’
argument is an analogy: just as false coins are only possible if there are true
ones around for comparison, false sense-data are only possible if there are true
sense-data around for comparison. All empiricists have to do is ensure they
are careful to work with the true ones rather than the false.
Descartes could reply to this latter objection by saying that he’s after total certainty
(because he is a foundationalist rather than someone like today’s scientific society
happy with the security of scientific knowledge) which cannot be delivered by senseexperience: just as even an expert cannot know for certain a particular coin is genuine,
we cannot know for certain which are our ‘true’ sense-data.
Meditation II
Archimedean point
Fixed locus from which the Earth itself can be moved: secure foundation.
Cogito ergo sum
It is logically impossible to doubt one is thinking (since a doubt is itself a thought).
This is proof against even the evil demon and provides a point of certainty: whenever
I am thinking, I must exist.
Subjective knowledge
This argument establishes the primacy of the subject (the individual mind) in
knowledge, i.e. rationalism is the route to true knowledge – so upsetting those who
believe that objective (empirical) knowledge is primary.
Substance dualism
The belief that that there are two substances in the world: physical stuff and mental
stuff.
Property dualism
The belief that there are two types of property in the world which are incompatible:
mental properties such as sensations and feelings; physical properties such as light
and sound.
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Sum res cogitans
‘I am a thinking thing’: my essence is that of a thinking thing: without thought, I
could not know that I exist. (Unlike my body which is not essential – I can exist
without it, in theory.)
Leibniz Law
Two things are identical if they have the same properties. Descartes claims that since
he cannot imagine his mind does not exist, but that he can imagine his body does not
existence, they have different properties and hence are different things
The Wax Argument
On heating, the properties of wax which I get through my senses all change. It is the
same wax because I understand it to be the same. Understanding is an attribute of the
mind. This understanding comprehends the infinite (of shape, of size of the wax)
which is impossible for the senses to do. Senses are linked to body/physical objects –
hence this is evidence for dualism.
Objections:

To know the Cogito, one must already know what are existence, thought and
logical entailment, i.e. it isn’t foundational at all.
 Knowledge is the exclusion of other possibilities – there is no meaningful
alternative to ‘I know that I think therefore I am’. Hence, it is not knowledge.
 It contains a suppressed premise (‘All thinking things exist’) which cannot be
known.
Descartes could reply that it is not a syllogism – that when you notice the single
example, this illustrates all examples (like in a maths proof).
 He cannot know that there is an ‘I’ – all he could claim is that ‘there is
thought’. He produces no evidence of the ‘self’ which has the mental
attributes he claims for it.
 Mental properties do not have to inhere in a ‘substance’.
 He cannot argue for dualism using Leibniz’ Law since he employs the
psychological verb ‘feign’ which is illegitimate.
 He cannot know his mind with the certainty he claims: conscious thoughts are
not sensibly definable within Descartes’ system.
 The attributes of wax are not conceived of in isolation as Descartes’ analysis
claims.
 Descartes has not given a positive explanation of mind and so cannot claim it
is better known than the body
Descartes could reply that the mind is unique and, as mental stuff, not open to the
same sort of mechanistic explanations that physical stuff is open to.
Meditation III
Clear and Distinct Perception
A thought about which one could not possibly be wrong (such as the Cogito); the
apprehension of this once the thought presents itself in the mind. Descartes uses it as
his criterion for the truth.
Idea
A thought which has an object. This is in contrast to two other mental events:
feelings and understanding. Ideas may be innate (carried within us from the start);
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adventitious (impressed on the mind from outside); factitious (synthesised in the
mind).
Objective reality
The notion that our mental events are real, but that they have different degrees of
reality. Descartes thinks that no particular mental event can have any more objective
reality than the mental event which caused it to arise.
Trademark (cosmological) argument
Given the notion of objective reality, and allowing that God is the superior mental
event that a mind can have, God the idea cannot have been synthesised by anything
less than God. Since Descartes has the idea of God, God must exist.
Cartesian Circle
Descartes’ critics say that his argument is circular and hence empty: ‘I am certain God
exists because I see it clearly and distinctly. I can be certain of what I see clearly and
distinctly because God exists.’
Epistemological necessity
For knowledge (beyond the bare Cogito) to be a possibility, God’s existence is
necessary. (Otherwise, scepticism via the evil demon possibility is always present.)
Objections:

‘truth consists in clear and distinct perception’ is hardly as plainly true as a
self-evident truth like 1 = 1 and so is not useful as a criterion for the truth.
Also, ‘self-evidence’ seems to vary from individual to individual; such truths
are not always immediately clear.
 It is rational to believe truths that are not self-evident so his criterion is far too
narrow.
 In the Trademark argument the premise about greater objective reality of the
‘causing’ thought relative to the ‘resulting’ thought is suspect: e.g. is the
thought of solidity caused by something more solid than the thought? Seems
highly doubtful.
 ‘Perfection’ as an idea can be arrived at more naturally by extrapolation from
our experience (e.g. such as a perfectly straight line).
 All cosmological arguments rely on the knowledge that ‘existence cannot
appear from nothing’ being already being in place before the argument can
take place (such as the ‘objective reality’ premise). This is not knowable a
priori (and Descartes hasn’t shown how he knows it) and so cannot be used to
produce the existence of God.
Descartes’ reply to the criticism of the circular argument accusation hinges on
memory: the evil demon can tamper with remembered thoughts, but not thoughts that
are being actively entertained at present. Current clear and distinct thought makes
memory (and hence the evil demon) to that thought (such as God’s existence)
irrelevant.
Meditation IV
Good God
Deceit is an imperfection and so could not be a part of the perfect God he knows.
Understanding
The ability to apprehend things clearly and distinctly. Since it can deliver the truth, it
is a perfect attribute. However, unlike God’s understanding, it is finite (Descartes
knows he doesn’t know everything).
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Will
The mental faculty for judging between things. This capacity can range unbounded
over all the possibilities that a mind can engender: it is infinite in its scope.
Error
Though possessing perfect gifts from perfect God (will and understanding), mistakes
can arise from judging outside the sphere of one’s understanding.
Objections:


Understanding is not immediate and universal – people vary in the degree to
which they ‘understand’ things. Without a sharp defining line, his appeal to
not judging outside the sphere of understanding is impossible.
It is impossible to withhold judgment in the way Descartes insists we must –
radically, we must judge whether we understand something clearly and
distinctly in the first place (which Descartes says we must do before we
judge…)
Meditation V
Res extensa
The ideas of material objects always carry with them attributes such as duration, size
and shape. Without the notion of dimension (of space/time), such ideas would be
impossible. Hence, the essence of the ideas of material things is extension.
Geometric truths
Truths about perfect triangles are possible despite not being prompted by anything
external to Descartes’ mind. In other words, truth can be derived from a concept.
Ontological argument
‘I have the concept of a supremely perfect being. Existence makes something more
perfect than non-existence. Hence it is contradictory to say that a perfect being does
not exist (and so a perfect being does exist.’
Objections:

Knowledge of ideas of physical objects must be a priori at this stage of
Descartes’ argument. He provides no justification for their being knowable in
this way.
 Defining something into existence is illegitimate (‘a T-fairy is a fairy that truly
exists. It is now contradictory to say ‘a T-fairy does not exist’ therefore Tfairies really do exist’ is plainly absurd.
Descartes replies that God is not like T-fairies. What makes God special is that he is a
unity that includes all the perfections. T-fairies and the like do not and hence for
them this proof is unavailable.
 The proof is illegitimate because it rests on a comparison of the imagined
existence and real existence – he has not shown that the mental world and the
real world are one and the same thing.
Meditation VI
Intellection
The process of the mind which leads to understanding.
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Imagination
Descartes’ term for mentally visualising some object or other.
Chiliagon argument
A thousand-sided figure is impossible to imagine and yet which can easily be grasped
by intellection. This demonstrates the difference between imagination and
intellection: imagination requires effort unlike intellection.
Natural light (or ‘by the light of nature’)
An alternative for clear and distinct perception (and which emphasises the nature that
God has made).
Imagination as an attribute of body
Descartes knows that extension is not essential to the mind. He also knows that
extension is essential to imagined objects (from Meditation V). Thus, imagined
objects cannot arise from the mind and so do arise from elsewhere: body.
Existence of physical objects
It is possible that these imagined objects are not real but this would involve God in a
deception. Since God is not a deceiver, physical objects (which give rise to the
imagined objects) exist.
Dualism argument
In a nutshell: it is possible for God to bring about any A and any B as distinct entities
if Descartes can perceive them as clearly and distinctly different. He clearly and
distinctly perceives mind and body as essentially different. Hence mind and body are
distinct entities.
Platonic dualism argument
The body is divisible; the mind is indivisible. This shows that they are separate
things.
Dualism and error
Given that God cannot make material things that are unextended, it is possible to
introduce error into the body (such as stimulating a nerve anywhere along its length
and the brain recording it as a stimulus applied at the – normal – end). This is not
God’s fault – especially as he has given us senses for checking such oddities and
understanding to find the truth.
Reliability of the senses
It is natural to trust one’s senses and, since it is God who created nature and
Descartes, the information from the senses can generally be trusted. God has done
what he can to make them reliable.
Memory
Knowledge of one’s past experiences and thoughts may be used to help filter
information from the senses to arrive at the truth.
Objections:



It is eminently possible for the mind to be the brain in operation. To prove
otherwise, Descartes must show that the mind operates in a different way from
any explanation of how the brain operates. This he fails to do. Indeed, the
mind and/or brain develop or deteriorate in step (‘instant idiot: just add
alcohol’) – an observation making dualism superfluous.
Though his chiliagon example is a good one, it is exceptional: there is not the
same clear-cut distinction between what can be thought and what can be
imagined.
His dualism argument only shows that mind-body separation are possible
rather than actual.
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In reply, Descartes would say that this is the point: they are separable (and hence
distinct) even if it is only as a possibility.
 His dualism argument rests on the reliability of his ‘clear and distinct
perception’ which is suspect (see above).
 It is possible that Descartes is not just a thinking thing (as per Meditation II),
his physical body may also be included in that essence. In other words, his
perception could be incomplete and there is no way that Descartes has shown
to demonstrate the limits of his clear and distinct perception lies solely with
the mind.
 As in Meditation II, Descartes provides no evidence that there is one mind per
body – and hence knowledge of the ‘self’ as commingled mind and body is not
possible.
 Descartes offers no coherent account of how the mind and the body could
possibly interact.
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