Is it metaphysics or epistemology?
Starting point is doubt - philosophy is too speculative.
He introduces radical skepticism.
But all things cannot be doubted. Search for certainty, rather than truth first.
Descartes employs systematic doubtfulness, which can be read as a suspension of metaphysics.
Descartes then introduces the hypothesis of a deceiving God to show one may also doubt this type of knowledge. “There is in my mind a certain opinion of long standing,” namely, the idea that God can do everything.
The experience of thinking itself, the thought of thought, is certain.
Descartes starts his argument with the following systematic doubt: If I am dreaming/deceived, then all my beliefs are unreliable. He then argues in the following steps:
We have access to only the world of our ideas; things in the world are accessed only indirectly.
These ideas are understood to include all of the contents of the mind, including perceptions, images, memories, concepts, beliefs, intentions, decisions, etc.
Ideas and the things they represent are separate from each other.
These represented things are many times "external" to the mind.
It is possible for these ideas to constitute either accurate or false representations.
God: Descartes’s argument for the existence of God consists in showing that a finite being could not have been the author of the idea of infinity. If I have the idea of infinity, then it can only be because God placed it in me, much as an artisan leaves a trace on his work. Descartes introduces the argument using a seemingly self-evident principle: “Now it is indeed evident by the light of nature that there must be at least as much (reality) in the efficient and total cause as there is in the effect of that same cause. For whence, I ask, could an effect get its reality, if not from its cause?”
Ego sum, ego existo. This is the first certitude of the thought that can doubt everything, except itself. Or, to be more precise, if it can doubt and be deceived, it can doubt everything except that it doubts and that it is.
Certitude of my existence: It presupposes an other who can deceive me, but one who must also exist if it is to deceive me.
Descartes says: “Then, too, there is no doubt that I am, if he is deceiving me. And let him do the best at deceiving me, he will never bring it about that I am nothing so long as I think that I am something."
"And certainly, because I have no reason for thinking that here is a God who is a deceiver [deceptor] [and of course I do not yet sufficiently know whether there even is a God], the basis for doubting, depending as it does merely on the above hypothesis, is very tenuous and, so to speak, metaphysical [a very pejorative use of the term!]. But in order to remove even this basis for doubt, I should at the first opportunity inquire whether there is a God, and if there is, whether or not he can be a deceiver. For if I am ignorant of this, it appears I am never capable of being completely certain about anything else."
"Several years have now passed since I first realized how numerous were the false opinions that in my youth I had taken to be true, and thus how doubtful were all those that I had subsequently built upon them. And thus I realized that once in my life I had to raze everything to the ground and begin again from the original foundations, if I wanted to establish [stabilire] anything firm and lasting in the sciences."(First Meditation.)
"Yesterday’s meditation has thrown me into such doubts that I can no longer ignore them, yet I fail to see how they are to be resolved. It is as if I had suddenly fallen into a deep whirlpool; I am so tossed about that I can neither touch bottom with my foot, nor swim up to the top. Nevertheless I will work my way up and will once again attempt the same path I entered upon yesterday. I will accomplish this by putting aside everything that admits of the least doubt, as if I had discovered it to be completely false. I will stay on this course until I know something certain, or, if nothing else, until I at least know for certain that nothing is certain." (Second Meditation)
"Archimedes sought but one firm and unmovable point in order to move the entire earth from one place to another. Just so, great things are also to be hoped for if I succeed in finding just one thing, however slight, that is certain and unshaken."
"Am I not at least something? But I have already denied that I have any senses and any body. Still I hesitate; for what follows from this? Am I so tied to a body and to the senses that I cannot exist without them? But I have persuaded myself that there is absolutely nothing in the world: no sky, no earth, no minds, no bodies. Is it then the case that I too do not exist? [This is the tipping point of the first, ontological, certitude, that of the Being of thought] But I assuredly was existing [eram]; if I persuaded myself of something."
"But there is some deceiver or other who is supremely powerful and supremely sly and who is always deliberately deceiving me. Then too there is no doubt that I exist, if he is deceiving me. And let him do his best at deception, he will never bring it about that I am nothing so long as I shall think that I am something. Thus after everything has been most carefully weighed, it must finally be established that this pronouncement “I am, I exist’ [ego sum, ego existo]” is necessarily true every time I utter it or conceive it in my mind."
“Now I will ponder more carefully to see whether perhaps there may be other things belonging to me (apud me alia sint) that up until now I have failed to notice. I am certain that I am a thinking thing. But do I not therefore also know what is required for me to be certain of anything?” (Meditation III)
What about thinking? Here I make my discovery: thought exists; it alone cannot be separated from me. I am; I exist—this is certain. But for how long? For as long as I am thinking; for perhaps it could also come to pass that if I were to cease all thinking I would then utterly cease to exist. At this time I admit nothing that is not necessarily true. I am therefore precisely nothing but a thinking thing [res cogitans]; that is, a mind, or intellect, or understanding, or reason—words of whose meanings I was previously ignorant. Yet I am a true thing and am truly existing; but what kind of thing? I have said it already: a thinking thing. (Descartes, “Meditations on First Philosophy,” 65 (AT, VII:26)
Momentary self-awareness? Is this just an anchoring point? How do we get from this grounding of philosophy to other insights?
Modern critiques: Today, Cartesianism has mostly negative connotations. It stands for a self-absorbed hypocritical thinking that disregards the world as pure extension (res extensa), matter without self-consciousness. For Descartes, the foundation is self-aware consciousness, in opposition to the rest of the world. Cartesianism is responsible for a profound misunderstanding of the place of the human being in this world. Our ecological catastrophe is preconfigured in Descartes.
Freudian revolution: Humans are built opposite to Descartes conception: Thoughts and feelings are primarily unconscious. The human mind is not a self-aware subject, it is a psychological machinery, with multiple modules that produces the sense of self. Our ego is an object of unconscious forces.