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Is Descartes' rational intuition and deduction thesis correct?
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Is Descartes' rational intuition and deduction thesis correct?
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Intuition and deduction thesis 25-mark essayThe intuition and deduction thesis is the claim made by Descartes and other rationalists that we can
have synthetic a priori knowledge, meaning knowledge referring to the way the world is deduced
independently of experience. Descartes presents his thesis to illustrate how we can acquire such
knowledge. He argues all knowledge rests on a priori foundations, derived from clear and distinct
ideas that we reach intuitively. Although Descartes can respond to Hume’s criticisms, I will argue
that his theory fails, namely because it is unable to respond to the cartesian circle.
Intuition is the ability to know something by thinking about it, whereas deduction is deriving true
propositions from other true propositions using reason. With deduction, a true conclusion must
follow from true premises. Descartes supports rational intuition and uses this method to reconstruct
his knowledge. He begins with clear and distinct ideas and the cogito (intuition). Clear and distinct
ideas refer to an idea presenting itself clearly in the mind. Descartes claims ‘I exist’ is a clear and
distinct idea. He proves it using the cogito, whereby Descartes proves his existence by thinking that
he must exist. Even to doubt his existence necessitates his existence as a doubting thing. So I exist
must be true.
Once proving his own existence, Descartes further argues for the existence of God. He puts forward
the trademark argument which rests on the causal adequacy principle. The CAP states that a cause
must contain at least as much reality as its effect. Descartes then asserted, as proved by the cogito,
that he exists as a finite and imperfect being, with the concept of God in his mind, who is an infinite
and perfect being. Applying the CAP, Descartes argues it would be impossible for him to have
created the cause of his idea. Only something equally as infinite and perfect, i.e. God, could’ve
implanted the idea, therefore God exists.
Hume’s bundle theory, if successful, would uproot the foundation for Descartes’ whole theory, and
so presents a real issue for rationalism. Empiricism claims knowledge of what exists must be a
posteriori, dependent on experience. Hume aims to dismantle the intuition and deduction thesis by
attacking the cogito. His criticism termed ‘bundle theory’ claims introspection cannot prove that we
are any more than a succession of thoughts. There is no discoverable ‘I’ or self, just a bundle of
abstract ideas and perceptions. The fact that we think does not mean to say that we are a thinker.
Descartes is mistaken. The following Descartes arguments rely on the cogito, so this is a considerable
criticism.
A response to this would be that Hume is misrepresenting Descartes’ theory (straw man fallacy),
since he makes no explicit claim that the self is inwardly discoverable. Descartes simply claims that it
is self-evident that it exists. He argues that there is something to experience these abstract thoughts
and perceptions. Even doubting suggests existence since the act of doubting requires an agent. It can
be concluded that Descartes can withstand this criticism on the grounds that his existence is self-
verifying, even if the ‘self’ isn’t directly discoverable.
Descartes then employs rational intuition and deduction to prove the existence of the external
world, as another example of synthetic a priori knowledge. He argued we are naturally inclined to
believe our senses are accurate in telling us the external world exists. If we were wrong about this, it
would entail deception. Descartes proved that God exists as a perfect being using the trademark
argument, and such an omnibenevolent being would not allow us to be deceived. If so, then our
senses must be correct in representing the external world, and so the external world exists.
Hume’s fork can be used to invalidate Descartes’ argument for God and therefore the external
world. His fork states that a statement must be either a matter of fact (empirically discoverable) or a
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