God could not deceive me, since this would imply an imperfection: "willful deception evinces maliciousness and weakness." Since God does not wish to deceive me, "he has not given me a faculty such that, when I use it properly, I could ever make a mistake."
But am I then incapable of erring? "I am subject to countless errors." I am a middle ground between the postive perfection of God and nothing ("what is supremely lacking in every perfection"). Since I lack many things, "it is not surprising that I am deceived."
Error is only a defect. My problem is that my faculty for judging the truth is not infinite. But why is my faculty of judging the truth not perfect of its kind?
What will is:
Indifference, i.e., not being moved by the superiority of one alternative to another, is the lowest level of freedom. If I were to see the good, we would freely move toward it. (This is similar to the views of Plato and Aristotle.)
Error arises from the fact that the will extends farther than the intellect, extending to things I do not understand.
We should be indifferent to those things we do not understand and embrace those which we do.
Why God is off the hook with respect to creating human beings capable of error:
The idea of continuous quantity is distinctly imagined, i.e., extension in length, breadth and depth. The parts of things have sizes, shapes, position and movements with durations. Learning about those things viewed generally is as if I already knew them. "That is, I first notice things that were already in me, although I had not directed a mental gaze toward them."
I have not produced some of these ideas, e.g. that of a triangle, since I can prove all kinds of things about them: the "nature, essence, or form is completely determined, unchangeable, and eternal."
Empiricism, the doctrine that all knowledge comes through sense-experience, is defeated: I can imagine all kinds of things about which there are demonstrations but which I have not experienced. "It is evident that everything that is true is something."
The notion that I can prove things from ideas I have suggests the ontological argument.
Certainly I discover within me an idea of God, that is, of a supremely perfect being, no less than the idea of some figure or number. And I understand clearly and distinctly that it pertains to his nature that he always exists, no less than whatever has been demonstrated about some figure or number also pertains to the nature of this figure or number. Thus, even if everything that I have meditated upon during the last few days were not true, I ought to be at least as certain of the existence of God as I have hitherto been about the truths of mathematics.
God without existence is like a triangle without the internal angles equalling 180 degrees or a mountain without a valley. A supremely perfect being would lack some perfection.
Objection: you still need the mountain to get the valley.
Response: Existence is inseparable from God, since I cannot think God without his existing. I am not free to think of God without existence.
"Because the necessity of this thing, namely of the existence of God, forces me to entertain the thought."
Objection: you need not have asserted that God has all the perfections.
Response: Although I need not have had the idea of God, once I did, I could see that God has all the perfections. The idea of God "is an image of a true and immutable nature."
The idea of God is implanted in me and not an invention.
The certitude of everything else depends on this, so that "without it I am unable ever to know anything perfectly." God buttresses conclusions I draw from my former clear and distinct perceptions. Even remembering that one had perceived something very clearly and distinctly is enough.
Descartes continues by explaining what it is to imagine something:
Imagining x = Understanding x + intuiting x as present "by my powers of discernment.
A triangle can be imagined, but a chiliagon (thousand-sided figure) can only be understood. A "peculiar sort of effort" is required to imagine, beyond what is required to understand.
The imagination is not essential to me: I would remain the same person without it. An explanation is given of why the imagination is not essential to the person: in understanding, the mind gazes on ideas in itself, whereas in imagination, the mind "intuits something in the body similar to an idea either understood by the mind or perceived by sense." But I still need a reason to think my body exists. Thus far it is still only probable, and I need a "necessary" conclusion.
The imagination dispensed with, does "the way of thinking that I call 'sense'" (see Med. 2) give us a reason to think bodies exist?
Here is Descartes' plan of attack in answering the question:
Since it seemed impossible that they come from myself, it remains that they come from other things, and the only kind that come to mind are those which resemble the ideas themselves.
One's own body seems in a privileged position, in that one can never separate one's self from it, and it is the seat of appetites, feelings, pleasure and pain. There is no evident connection between feelings of hunger and the nourisment of bread. I have only been taught so by nature.
Regarding the second point, Descates advances the problem of "perceptual relativity": "judgments of the external senses deceived me" and internal senses are deceived by pains in amputated limbs.
Add to this list "two quite general" reasons.
Regarding the third point, what God can make separately is different from something else. God can make what I clearly and distinctly understand, so if they can be separated in thought, they are distinct. I am distinct from my body because I can think of myself as distinct from it: my essence is only as a thing that thinks and not as an extended thing.
Imagining and sensing are not of my essence but depend on me. They are distinguished from me in the manner of modes.Moving and changing shape cannot exist without corporeal substances, but can exist apart from thinking substances.
I cannot use my faculty of sensing unless "there also exists, either in me or in something else, a certain active faculty of producing or bringing about these ideas." But the faculty is not in me "since it clearly presupposes no intellection, and these ideas are produced without my cooperation and often against my will." So it is in a substance which contains the objective reality of the idea formally (body) or eminently (God). "But, since God is not a deceiver, it is absolutely clear that he sends me these ideas neither directly and immediately--nor even through the mediation of any creature, in which the objective reality of these ideas is contained not formally but only eminently." This is because God made we with "a great inclination to believe that these ideas proceeded from corporeal things."
Everything that I clearly and distinctly understand "that is encompassed in the object of pure mathematics" is in the bodies, though other things in the idea may be confused. What about the mathematical particulars (size of sun) or what is less understood (secondary qualities)? Nature (God's creation) tells me that I have a body which feels pain, hunger, etc. "Therefore, I ought not to doubt that there is some truth in this."
I must be mingled together with the body to feel, rather than just understand, my pain. But not as a seaman in a ship, since I would perceive myself detatchedly and more clearly. Instead, the mingling is the source f confusion.
Nature teaches me of the existence of other bodies as well. It also teaches that there are differences in bodies correlated to those in my perception, though not necessarily similar to them.
We must distinguish the teachings of nature from "a certain habit of making unconsidered judgments."
Only what is agreeable or disagreeable to the composite of mind and body is taught to me by nature. Yet the senses are used as "certain rules for immediately discerning" what the essence is of bodies external to us.Man is a limited being, so he can make mistakes about what nature teaches (sugarūcoated poison). Still, we err even in what nature impels us to do. It would be "a true error of nature that this [dropsical] body should thirst when a drink would be harmful to it." The claim that this is a turn away from my true nature is defeated on the grounds that this is an arbitrary sense of 'nature'. In the full sense, I take what nature teaches me to contain some truth, so nature is deceptive in the case of dropsy. How could God permit this?
The mind is indivisible, one complete thing, while bodies, including mine, are divisible. The body is not immediately affected by all the parts of the body. Only the part of the brain where the "common sense" is found is affected. It can be in the same state with different affections in the body, as experiment shows. The parts in between masquarade as the source. The fact that the natural inclinations work right most of the time attests to God's craftsmanship. It is better that they break down sometimes than that they never work at all.We can, anyway, correct errors, using multiple senses, as well as memory and intellect.
The dream argument can now be rejected. "For I now noticed that a very great difference exists between these two; dreams are never joined with all the other actions of life by the memory, as is the case with those actions that occur when one is awake." I can have certainty" when I connect perceptions "without any interruption with the rest of my life."
But life is short; we leave ourself open to error, and "we must acknowledge the infirmity of our nature."