But there is so much to accomplish before the question can even be asked. Like determining what the mind actually is.. and, moreover, whether it is. At first, it seems as though 'proving' that the mind exists is far more difficult than convincing someone that the physical world does. But that isn't so.
Descartes' Meditations (clearer translation) offer arguments that simultaneously show the certainty of the mind and its states and the unsure nature of the physical world. Here is an overview:
"Surely whatever I had admitted until now as most true I received either from the senses or through the senses. However, I have noticed that the senses are sometimes deceptive; and it is a mark of prudence never to place our complete trust in those who have deceived us even once." (meditation 1)
This is a tiny argument that posits doubt in the senses and their ability to convey knowledge. He gives two examples of senses deceiving: madmen and dreaming. He then gives an argument to show that an omnipotent God or an "evil genius" could be constantly deceiving us (evil genius thrown in because he does not accept that God's goodness would provide for that. however, he must question why God allows deception at all and chooses to ignore it.) through both our mind and our senses. These arguments and examples show the uncertain nature of the physical.
The fourth example that he gives is a thought experiment used to illustrate the reality of the mind versus physical reality (this morphs later into objective and formal reality). A thought experiment is just like a real one; it takes an assumption and uses an example to determine its truth value. Descartes' assumption is this: the physical has more reality than the mental.
"Let us consider those things which are commonly believed to be the most distinctly grasped of all: namely the bodies we touch and see." (all following quotes from med. 2)
He doesn't mean to prove this, of course--the experiment is a reductio ad absurdum. So Descartes allegedly picks up a piece of wax and examines it. He describes it (physically): "...it is quite fresh, having been but recently taken from the beehive; it has not yet lost the sweetness of the honey it contained; it still retains somewhat of the odor of the flowers from which it was gathered; its color, figure, size, are apparent (to the sight); it is hard, cold, easily handled; and sounds when struck upon with the finger. In fine, all that contributes to make a body as distinctly known as possible, is found in the one before us."
He has shown, then, that everything--haha--to be known about the wax can be known via the senses. He then demolishes every piece of perception that was just established--
"But...let it be placed near the fire--what remained of the taste exhales, the smell evaporates, the color changes, its figure is destroyed, its size increases, it becomes liquid, it grows hot, it can hardly be handled, and, although struck upon, it emits no sound. Does the same wax still remain after this change? It must be admitted that it does remain; no one doubts it, or judges otherwise. What, then, was it I knew with so much distinctness in the piece of wax? Assuredly, it could be nothing of all that I observed by means of the senses, since all the things that fell under taste, smell, sight, touch, and hearing are changed, and yet the same wax remains."
And so we have a problem. What is it, if not all these things? By asking what it IS, he is asking what kind of reality it has, what kind of existence. Physical reality seems to be fleeting and evasive and uncertain.
"Perhaps the wax was what I now think it is: namely that the wax itself never really was the sweetness of the honey, nor the fragrance of the flowers, nor the whiteness, nor the shape, nor the sound, but instead was a body that a short time ago manifested itself to me in these ways, and now does so in other ways. But just what precisely is this thing that I this imagine?"
Did you see the shift? He shows that it can't possibly BE any of the qualities.. so he 'imagines' it. He just shifted the reality of the thing to something mental instead of something physical. I thought it was pretty smooth (pun intended.)
"..see what remains after after we have removed everything that does not belong to the wax: only that it is something extended, flexible, and mutable."
These are the only things left that he can perceive about the wax. He shows, at slight length, that he cannot imagine these qualities, so they must be perceived by the mind. Read the text for the connective arguments.
"It remains for me then to concede that I do not grasp what this wax is through the imagination: I perceive it through the mind alone."
And so the mental has more reality than the physical. And we know that clearly and distinctly. Lesson of the day, eh? I like it.
In any case, my interest is more in the reflexive nature of mental states (ie doubting, understanding, affirming, denying...) and how that shows the certainty of the mind. Digression: And what of belief and its object? Descartes shows the existence of God.
Unfortunately, I do have an idea of my dirty dishes... and cannot deny that they have objective reality. But how much reality can the mind give an idea? Tune in to the link above to Meditation III, which uses this question to its advantage re: the infinite. That is, God.
