Meditations on First
Philosophy
Summary of
Descartes’ arguments
Meditation I
• 1. A firm foundation for the sciences
requires a truth that is absolutely certain; for
this purpose, I will reject all my beliefs for
which there is even a possibility of doubt,
and whatever truths are left will be
absolutely certain.
I continued
• 2. To this end it is not necessary to go
through all my beliefs individually, since
they are all based on a more fundamental
belief. If there is any reason to doubt this
foundation belief, then all the beliefs based
on it are equally doubtful.
Meditation I continued
• 3. All my beliefs about the world are based on the
fundamental belief that the senses tell me the truth.
But this belief is not absolutely certain. It is at
least possible that everything my senses tell me is
an illusion created by a powerful being. Therefore,
there is some reason to doubt my foundation
belief, and thus all my beliefs about the world are
doubtful; none of them can serve as the foundation
for science.
Meditation II
• 1. If all my beliefs about the world are doubtful, is
there any truth which can be absolutely certain?
Yes. Even if all of my experience is an illusion, it
cannot be doubted that the experience is taking
place. And this means that I, the experiencer, must
exist.
2. Since the only evidence I have that I exist is that
I am thinking (experiencing), then it is also
absolutely certain that I am a thing that thinks
(experiences), that is, a mind.
Meditation II continued
• 3. Since I am not certain (yet) that the physical
world (including my body) exists, but I am certain
that I exist, it follows that I am not my body.
Therefore, I know with certainty that I am only a
mind.
4. I am much more certain of my mind's existence
than my body's. It might seem that in fact we
know physical things through the senses with
greater certainty than we know something
intangible like the mind.
Meditation II continued
• But the wax experiment demonstrates that
the senses themselves know nothing, and
that only the intellect truly knows physical
things. It follows that the mind itself is
known with greater certainty than anything
that we know through the senses.
Meditation III
• 1. Every idea must be caused, and the cause must
be as real as the idea. If I have any idea of which I
cannot be the cause, then something besides me
must exist.
2. All ideas of material reality could have their
origin within me. But the idea of God, an infinite
and perfect being, could not have originated from
within me, since I am finite and imperfect.
III continued
• 3. I have an idea of God, and it can only
have been caused by God.
• 4. Therefore God exists.
Meditation IV
• 1. Only an imperfect (less than perfectly good)
being could practice deliberate deception.
Therefore, God is no deceiver.
2. Since my faculty of judgment comes from God,
I can make no mistake as long as I use it properly.
But it is not an infinite faculty; I make mistakes
when I judge things that I don't really know.
IV continued
• 3. God also gave me free will, which is
infinite and therefore extends beyond my
finite intellect. This is why it is possible to
deceive myself: I am free to jump to
conclusions or to proclaim as knowledge
things that I don't know with absolute
certainty.
IV continued
• 4. I therefore know now that if I know
something with absolute certainty (clearly
and distinctly), then I cannot be mistaken,
because God is no deceiver. The correct
way to proceed is to avoid mistakes and
limit my claims to knowledge to those
things I know clearly and distinctly.
Meditation V
• 1. Now I want to find what can be known for
certain about material objects. Before deciding
whether they exist outside me, I know that my
ideas of them consist of shape, size, motion, etc. I
also know that by thinking about these attributes I
can discover certain facts that are necessarily true
about them (the truths of geometry, for example).
2. I do not invent ideas such as geometrical
shapes, nor do I get them from sensory experience.
Proof of this is the fact that I can discover
geometrical truths about figures which I cannot
imagine.
V continued
• 3. Just as, by thinking about my ideas of
geometrical shapes, I can discover truths
that necessarily belong to them, I can do the
same with God. I have a clear and distinct
idea of a perfect being. Perfect = lacking
nothing. I cannot conceive of a being that is
perfect but lacks existence. Therefore,
existence necessarily belongs to God.
V continued
• 4. This doesn't mean that my thinking of
something makes it exist. If I conceive of a
triangle, I must conceive of a figure whose angles
equal two right angles. But it doesn't follow that
the triangle must exist. But God is different. God,
being perfect, is the one being to whom existence
must belong. Thus, when I conceive of God, I
must conceive of a being that exists.
V continued
• 5. Because God, being perfect, is not a
deceiver, I know that once I have perceived
something clearly and distinctly to be true,
it will remain true, even if later I forget the
reasoning that led me to that conclusion. I
could not have this certainty about anything
if I did not know God.
Meditation VI
• 1. All that is left is to determine whether material
objects exist with certainty. I know that the
abstract shapes representing them are real, since I
perceive them clearly and distinctly in geometry.
2. Furthermore, I have a faculty of imagination, by
which I can conceive of material objects, and
which is different from my intellect. That it is
different is proven by my ability to do geometry
with unimaginable figures. Only intellect is
necessary for my existence.
VI continued
• 3. The most likely explanation for the existence of
my faculty of imagination is that my mind is
joined with a body that has sense organs. This is
even more likely in the case of the faculty of
sensation.
4. It formerly seemed that all my knowledge of
objects came through the senses, that their ideas
originated from and corresponded to objects
outside me. It also seemed that my body belonged
especially to me, although I did not understand the
apparent connection between mind and body.
VI continued
• 5. Then I found it possible to doubt everything.
Now I am in the process of systematically
removing doubts where certainty exists.
6. Now that I know God can create anything just
as I apprehend it, the distinctness of two things in
my mind is sufficient to conclude that they really
are distinct. Thus I know I exist, I am a thinking
thing, and although I may possess a body, "it is
certain that this I is entirely and absolutely distinct
from my body, and can exist without it."
VI continued
• 7. My faculty of sensing is passive and thus
presupposes a faculty of causing sensation, which
cannot be within me, since some ideas come to me
without my cooperation and even against my will;
it therefore belongs to something else. This is
either a body or God. But since God is not a
deceiver, he doesn't plant these ideas directly in
me (doesn't make me believe in a nonexistent
world). Therefore corporeal things exist. My
senses might mislead me about the details, but I
know at least that the ideas that I clearly and
distinctly understand--geometrical properties-belong to these bodies.
VI continued
• 8. Nature is God's order; thus it has truth to
teach me. For example, that I am present to
my body in a more intimate way than a pilot
in a ship. And that there are other bodies
around me that affect me in various ways,
that should be pursued or avoided; the
senses thus act to preserve and maintain the
body.
VI continued
• 9. But I also make some judgments on my own
that are not justified by nature's teachings,
particularly in assuming objects and their qualities
to be exactly as my senses report them, that sense
qualities reside in them, etc. It is the fault of my
judgment that I use sense perception as a direct
apprehension of the essences of external bodies;
there is nothing inherently deceptive about
sensation.
VI continued
• 10. Another problem is the misleading signals I
sometimes get from my own body, which induce
me to commit errors. A body with edema, for
example, will have an inclination to drink, when in
fact this is something it ought to avoid. How can
God permit this?
11. The body is divisible, the mind is not. Further,
the mind gets impressions from the parts of the
body not immediately, but via the brain.
VI continued
• 12. By using more than one sense, and memory, I
can avoid errors of the senses of this kind. So I
should get rid of the excessive doubts I started
with, especially those premised on dreaming, since
I can easily distinguish dreaming from waking by
the continuity of the latter. I can trust the truth of
my ideas as long as my senses, memory, and
understanding are all consistent with one another.
Close the book
Questions??