Summary of Descartes' Meditations on First
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
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
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.
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.
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. 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.
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
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.
3. I have an idea of God, and it can only have been caused by God. Therefore
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.
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.
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.
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.
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.
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
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.
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
Only intellect is necessary for my existence.
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.
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."
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.
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.
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
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. Therefore the
nerves running from the parts to the brain might be stimulated (pulled)
somewhere in between, registering motion in the brain just as if the body part
were affected. When everything functions normally, the sensations in the mind
are the best and most appropriate for the purpose of maintaining health. So
the exceptions prove the goodness of God in making us this way.
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
Copyright © 1999 James T. Anderson