The argument for universal doubt:
A. The dream argument:
1. I often have perceptions very much like the ones I usually have in sensation while I am dreaming.
2. There are no definite signs to distinguish dream experience from waking experience.
therefore,
3. It is possible that I am dreaming right now and that all of my perceptions are false
B. Objection to the dream argument:
1. It could be argued that the images we form in dreams can only be composed of bits and pieces of real experience combined in novel ways.
therefore,
2. Although we have reason to doubt the surface perceptual qualities of our perception, we have no reason to doubt the properties that we perceive the basic components of our experience to have. (In particular, there is no reason to doubt the mathematical properties that material bodies in general have.)
C. The deceiving God argument:
1. We believe that there is an all powerful God who has created us and who is all powerful.
2. He has i in his power to make us be deceived even about matters of mathematical knowledge which we seem to see clearly.
therefore,
3. It is possible that we are deceived even in our mathematical knowledge of the basic structure of the world.
D. Objections to the deceiving God argument:
1. We think that God is perfectly good and would not deceive us.
2. Some think that there does not exist such a powerful God.
E. Replies:
1. If it were repugnant to God's nature to deceive us, he would not allow us to be deceived at all.
2. If there is no God, we must assume the author of our being to be even less perfect, so that we have even more reason to doubt all our beliefs.
F. The demon argument:
1. Instead of assuming that God is the source of our deceptions, we will assume that there exists an evil demon, who is capable of deceiving us in the same way we supposed God to be able
Therefore, I have reason to doubt the totality of what my senses tell me as well as the mathematical knowledge that it seems I have.
The Argument for our Existence (the "Cogito"):
1. Even if we assume that there is a deceiver, from the very fact that I am deceived it follows that I exist.
2. In general it will follow from any state of thinking (e.g., imagining, sensing, feeling, reasoning) that I exist. While I can be deceived about the objective content of any thought, I cannot be deceived about the fact that I exist and that I seem to perceive objects with certain characteristics.
3. Since I only can be certain of the existence of myself insofar as I am thinking, I have knowledge of my existence only as a thinking thing (res cogitans).
The Argument that the Mind is More Certainly known than the Body:
1. It is possible that all knowledge of external objects, including my body, could be false as the result of the actions of an evil demon. It is not, however, possible that I could be deceived about my existence or my nature as a thinking thing.
2. a. Even Corporeal objects, such as my body, are known much more distinctly through the mind than through the body.
The wax argument for (2a):
i. All the properties of the piece of wax that we perceive with the senses change as the wax melts.
ii. This is true as well of its primary properties, such as shape, extension, and size.
iii. Yet the wax remains the same piece of wax as it melts.
therefore,
iv. Insofar as we know the wax, we know through our mind and faculty of judgment, not through our senses or imagination
b. Therefore, every act of clear and distinct knowledge of corporeal matter also provides even more certain evidence for the existence and nature of ourselves as thinking things.
Therefore, our mind is much more clearly and distinctly known to us than our body.
I. Meditation Three: Descartes proves God's existence and that He is not a deceiver, thereby allowing us to be sure that we are not deceived when we perceive things clearly and distinctly.
A. Summary of things of which I am certain and those which I still must doubt.
1. I am certain that I exist as a thinking thing.
2. I must still doubt both my senses and my intuitions concerning mathematical knowledge since God may have constituted me so as to be deceived even about those things I seem most certain.
Therefore, in order to become certain of anything else I must inquire into the existence of God and see whether He can be regarded as a deceiver.
B. Preliminary Discussion of Ideas
1. I have ideas that are like images of things. The most common cause of error is the judgment that these ideas are similar to things that exist outside of me.
2. There are three possible types of ideas: innate, those that originate in myself, and those that originate from something outside of me. We shall be most interested in the latter group.
3. Even though some ideas of apparent external objects come to me against my will, I cannot regard them as corresponding to external things. This is because:
a. I may have some faculty which produces these ideas.
b. Even if they come from outside me, I have no guarantee that they are similar to their causes.
Therefore, the principle upon which I have judged my ideas to be similar to external objects seems to be mistaken.
C. The argument for the existence of God from the fact that I have an idea of Him.
1. Besides its formal reality, which accounts for its mere existence as an idea, every idea also has objective reality according to the reality of the thing which it represents, or its object.
2. There must be as much reality in the cause as there is in the effect. This applies to objective reality as well as formal reality.
3. I need not assume a cause greater than myself for any of my ideas of corporeal substance nor of other people or angels.
4. I have an idea of a perfect God, and this idea has more objective reality than any idea of a finite substance.
5. The idea of God could not have originated in me, since I am a finite substance.
Therefore, God must exist as the only possible cause of the objective reality found in my idea of Him.
D. Objections to the argument and replies.
1. Perhaps our idea of God is gotten from a negation of our limited properties.
Reply - We must have an idea of perfection before we can have an idea of limitation.
2. Perhaps the idea of God is materially false.
Reply - The idea of God is the most clear and distinct of our ideas.
3. Perhaps I am more perfect than I think and contain the perfections I attribute to my idea of God potentially.
Reply - Potential reality is not enough to cause the objective reality of my idea, and I will never have the actual perfection needed since I am a finite being, always capable of improving
E. The argument from my existence: It can also be argued that a cause more perfect than myself must be assumed to explain my coming into being and my continued existence. This cause must be God.
F. Objections to the argument from my existence.
1. Why must this more perfect being who is the cause of my idea of God and of my existence be taken to be God?
Reply - Any finite cause must itself be caused by something else and the regress must end a some point with an infinite or perfect cause.
2. Why cannot there be several partial causes for my existence?
Reply - Unity is one of the main perfections in my idea of God; this must have been caused by a unified being.
G. God cannot be seen as a deceiver, since He is perfect and deception depends upon some defect.
II. Meditation Four: Descartes explains the possibility of error.
A. I know that God is not a deceiver and that God also created me along with all my capacities. I also know that I am often in error. This error cannot be due to the correct operation of any faculty which God has created in me, for this would make God a deceiver. I must inquire, therefore, into how it is possible that I can err even though I am the product of a benevolent God.
B. Error is due to the concurrent operation of the will and the intellect. No error is found in the intellect. Error consists in the will, in its judgments, going beyond what the intellect clearly and distinctly perceives to be the case.
C. God cannot be blamed for giving us a free or unlimited will which it is possible for us to abuse and thereby fall into error.
D. The way to avoid error is to refrain from judgment until our intellect sees the truth clearly and distinctly.
III. Meditation Five: Descartes considers what properties we can know to belong to the essence of material things and also considers another way of proving God's existence by considering what properties we can know to belong to God's essence.
A. When I examine those ideas of corporeal objects that are distinct and not confused, I find that these are properties concerned with extension and duration: length, breadth, depth, size, shape, position, and movement.
1. When I discover particular things about these properties, it seems as if I am recalling something I already knew, something already within me.
2. Although they seem to be already in me, I am not the source of these ideas: they have their own immutable natures which would be the same whether or not I existed, or whether there exists any object that corresponds to these ideas.
3. Neither do these ideas come to me through the senses: I can form an idea that it is impossible to imagine or sense (such as the thousand sided figure mentioned in Meditation Six) and demonstrate many necessary truths concerning its nature.
B. The Ontological Argument for God's existence.
1. We have as a general principle that when I consider an idea, all that I perceive clearly and distinctly as pertaining to that thing really does pertain to it.
2. I understand clearly and distinctly that necessary existence belongs to the essence of God.
3. Therefore, existence really does belong to the essence of God and, hence, God exists.
C. Objections to the argument.
1. In all other cases we separate existence from essence.
Reply - It is impossible to conceive a perfect being as lacking a perfection, existence.
2. Granted that we cannot think of God except as existing, still our thought does not make him exist.
Reply - It is the necessity of God's existence that imposes the necessity on our thought, not the other way around.
3. We need not assume that God has all perfections, including existence.
Reply - It is impossible in conceiving a supreme being to avoid attributing all perfections to Him.
D. The role of God in making knowledge possible.
1. Even though we naturally take those things we perceive clearly and distinctly to be true, if I were ignorant of God I could still find reason to doubt these things once my attention was not fixed firmly on their demonstration.
2. In particular I might think that I was constituted so as to be deceived about things that I believe I see quite evidently.
3. Once we are aware of God's existence and that he cannot have made us so as to be deceived about what we see clearly and distinctly, we cannot be deceived as long as we assent only to what we see clearly and distinctly. It does not matter if we are in fact dreaming; what our intellect tells us is wholly true.
4. Therefore, the truth and certainty of every science depends upon the knowledge of God.
On the Distinction of Mind and Body and the Existence of Material Objects
I. Introduction to the problem of the existence of material things.
A. I know that material objects exist insofar as they are objects of pure mathematics, since I clearly and distinctly perceive the mathematical primary properties of corporeal objects.
B. It also seems that my imagination gives me evidence of the existence of external objects. Therefore, we must investigate this faculty.
II. The distinction between Imagination and Intellect.
A. When I imagine something, I intuit that thing as present to my mind.
B. Imagination is thus distinct from thought since I can think of things without intuiting them as present. An example is a thousand sided figure, the chiligon. I can think of this even though I cannot form an image of it.
C. Effort is required for imagination, while it does not seem to be for Thought.
D. The faculty of Imagination is not essential to me. I can exist without this faculty.
E. In thought the mind turns on its own ideas. In imagination the mind turns toward the body.
Therefore,
F. The imagination seems to require the existence of the body, but this is only a probability. We cannot yet say certainly that a body exists.
III. The evidence for the existence of corporeal things from the senses.
A. Summary of old beliefs that I got from the senses: all of my impressions of the secondary properties of objects.
B. Reasons for thinking that these showed the existence of objects.
1. These ideas appeared against my will.
2. They are more vivid than those ideas I imagine.
3. All of the ideas that I form through imagination are composed out of components that come from the senses. Nothing is in the imagination that was not first in the senses.
4. I sense pain and pleasure in my body, but not in objects external to me.
C. Reasons for doubting that these things show that material objects exist.
1. The senses often show things to me about objects hat I know cannot be true. For example, a tower in the distance seems round when in fact it is square.
2. People sometimes fell pain in limbs that have been amputated, so the feeling of pain in our body gives no evidence for its existence.
3. It may be possible that I am dreaming.
4. I may be constituted by nature so as to be deceived about things I think I see clearly.
5. There may be some unknown faculty in me that produces these ideas in me even against my will.
IV. The argument for the distinction of mind and body and the existence of material objects.
A. The distinction of mind and body.
1. The argument from knowledge.
a. If I clearly and distinctly understand one thing as distinct from another it is so.
b. I am certain that I exist as a thinking thing, while I am not certain of the existence of my body.
Therefore,
c. I am a thinking thing and nothing else. My mind is distinct from my body.
2. The argument from extension.
a. I am a thing that thinks and not an extended thing.
b. I have a distinct idea of body as an extended thing.
Therefore,
c. My mind is distinct from my body.
B. The argument that material objects exist.
1. I can understand myself without imagination and sense, but I cannot understand imagination and sense without attributing them to a thing that thinks.
2. Movement is a power of mine, but movement is a power only of extended things
Therefore,
3. It seems that although I am essentially a thinking thing, I am not only a thinking thing. It at least seems to me that I also have an extended body, but we must now see how we can be certain of this.
4. I not only have the power of passive sense, of examining the contents of my mind, but I also have active sense, the power of originating ideas within my mind. This faculty of active sense cannot be within me for two reasons:
a. No intellection is required for this active sensing.
b. These ideas come to me by active sense against my will.
Therefore,
5. This faculty is in a substance other than myself.
6. This substance much have as much reality as the objective reality of the ideas it produces.
Therefore,
7. This substance must be either God or an external extended body.
8. God is no deceiver.
9. He created me and gave me a great inclination to believe that these ideas come from corporeal things.
10. If they do not come from external objects, then God must be a deceiver. But this is an absurdity.
Therefore,
11. Material objects exist.
C. These objects, however, may not be as they seem to us through the senses.
Having established the existence of external objects, Descartes goes on to consider whether our senses tell us the truth about them.
V. The relation of Mind and Body.
A. I am intimately joined with my body. Feelings of pain and pleasure are confused modes of perception arising out of my union with the body.
B. We have many ideas from sense, but our nature does not teach us to conclude anything from these unless there is an inquiry by the intellect. Mind, not the composite of mind and body is capable of knowing truth.
Therefore,
C. The senses tell us only what is necessary for the welfare of the composite of mind and body.
D. With respect to the essences of things the senses are confused.
E. The poison objection: It would seem that it some cases our senses do not tell us what is best for the welfare of our body. For example, many poisons seem attractive to the senses, or an ill person may desire something injurious to her.
VI. Is God, therefore, to blame for giving us sensory faculties that sometimes lead us into harm?
A. The body is like a machine.
B. Mind and Body are distinct. This can be seen by noting that mind is indivisible, while body is divisible.
C. Mind is affected only by the brain, so all signals from the body must travel up into the brain.
D. Signals travel to the brain from the periphery of our body by means of animal spirits, so the system is like a cord running to the brain which can be pulled at any point along its length. Thus we can get signals in the brain that do not originate in our senses, but which we perceive as doing so.
Therefore,
E. Even though this is the best possible arrangement to protect our body, it is possible to be deceived by a cause of a disturbance in our animal spirits within our body rather than outside it. Thus God cannot be blamed for this arrangement.
VII. Being aware of this arrangement, I can use memory and intellect to avoid error by restricting my judgment to those things I perceive clearly and distinctly. We can return all those beliefs which we formerly took as doubtful, while disposing of those which led us astray.