DESCARTES:
MEDITATION 3
OR: THE WORLD REGAINED —
WITH CERTAINTY(?)
Proving he’s not
systematically decieved
God has
existence
just as
necessarily
as triangles
have three
sides.
THE CARTESIAN CIRCLE
Can we use reason to remove doubts
about the soundness of our reason?
Descartes says at start of Meditation 3:
“So I now seem to be able to lay it down
as a general rule that whatever I
perceive very clearly and distinctly is
true”
…but then raises doubts….
Form of Argument as a Whole 1
i) I exist 
ii) I have idea of perfect
being 
iii) Only possible cause of
this idea is actual perfect
being (aka God) …
Form of Argument as a Whole 2
iv) God exists 
v) God would not allow me
to be systematically
deceived, because
vi) deception “depend[s] on
some defect” (180L) 
Form of Argument as a Whole 3
vii) Malicious Demon
impossible 
viii) The world exists [more
or less] as revealed by my
senses+reason [I am not
systematically deceived].
CRUX OF ARGUMENT
iii) Only possible cause of
the idea of God is God.
Subargument: Paragraph
beginning “Now it is
manifest…” (175R)
CRUCIAL INFERENCE
“…in order for a given idea to
contain such and such
objective reality, it must surely
derive it from some cause
which contains at least as
much formal reality as there is
objective reality in the idea.”
TWO KINDS OF REALITY
Objective Reality: reality of
the object in the idea
Formal Reality: the reality of
the object outside mind
Presupposed logic
Ideas [eidos]
are copies [forms]
of real things.
Idea of x = form (shape, structure)
of x copied in the mind—minus
the matter or substance of x.
Formal/Objective Examples
Descartes’ examples
stone –causes stone
heat –causes heat
Other (better?) examples
infinity –causes infinity
perfection–causesperfection
Sub-Argument 1
Three sources of ideas (174R):
innate
adventitious
fictitious
Sub-Argument 2
Principle of Sufficient Reason:
“something cannot arise from
nothing”
or ex nihilo nihil fit
or “everything has a cause”
(175R)
Sub-Argument 3
The idea of God is not formed by
“negating the finite” (177L)
We have a “positive” idea of the
perfect being, not merely a
“negative” one.
Sub-Argument 4
I am not source of idea:
my perfections merely
potential, whereas God’s
are actual (178L)
Sub-Argument 5
The idea of God is innate.
(179R)