René Descartes (1596-1650)
• Father of modern rationalism.
• Reason is the source of knowledge, not
experience.
• All our ideas are innate.
• God fashioned us with these ideas.
• We discover basic truths by intuition: by
grasping basic connections between the ideas
we have.
• We deduce or demonstrate more complex
truths.
Aim and method
• Descartes wants knowledge.
• He knows that he has many false beliefs.
• He needs to weed them out to establish base of indubitable,
necessarily true beliefs.
• Foundationalism – basic beliefs provide the ultimate source of
justification.
• His method is to challenge each thing he believes to see whether it
is “completely certain and indubitable”. This is known as the method
of doubt.
• Key reading – Ch. 4; Meditation 1.
Scepticism: Wave I
The sceptic says:
knowledge is impossible!
What does this show? Simply that there is a
reality and something we could have true
beliefs about. But without a test, we can’t
know which beliefs are true. So, there’s no
way out of the sceptical problem here.
So, all that I believe could
be false?
Surely not! A mistake can
only exist where there is
truth or correctness.
A counterfeit £10 can exist
because there are real
ones. A counterfeit £15 note
can’t.
A test can only have wrong answers if there
are right answers too.
Scepticism: Waves II and III
The sceptic says: knowledge is
impossible!
…and so on, forever. So, even if
there were a test, it would be of no
use!
Could there not be a test to
prove whether I am in the
Matrix?
…but then how can I be sure I am
really performing T*? I would need
another test, T**…
Let’s suppose so: a test T.
I carry out T to determine whether I
am in the Matrix…
I would need another test T* to
check that I was performing the first
test, T, correctly…
…or do I? How can I be sure I
really did the test instead of being
fooled into thinking I did it?
Cogito and Self
Not reason that tells me –
awarneess.
I am a brain./
The Empiricist Hume
will later argue that
Descartes is wrong.
Descartes and the wax
All I can know are the
surfaces of things: what
my senses tell me.
I simply come to
believe that, despite
changes in
appearance, there is
still the same wax
because this simplifies
my understanding of
the world.
Consider a game
like Call of Duty. All
I see is a twodimensional grid of
pixels…
But my mind interprets certain
arrangements of pixels as
three-dimensional objects,
even though there are no such
things really there.
In the same way, perhaps I interpret reality as a three-dimensional world of objects as
this is a simpler explanation. It would be impossible to cope if I thought everything was
always changing.
Descartes and God: The Ontological Argument
Philosophers
such as
Gassendi, Kant
and Russell
claim this
argument does
not work.
A real football
doesn’t have an
extra property
of existence.
What makes
(e.g.) a football
what it is are
properties such
as being
spherical and
being bouncy.
Existence isn’t
a property. It
doesn’t make
anything the
sort of thing it
is.
A real
football is
just as much
a football as
an imagined
one.
So, we can’t
say God has
this property
either. What
makes God
God are
properties such
as:
…omnipotent.
…omniscient.
…omnibenevolent.