After the First Meditation, the Meditator feels totally confused, as though he has “fallen unexpectedly into a deep whirlpool” and can’t tell which way is up and which is down. If he can’t trust anything he sees or remembers, can he really know anything for sure? Yes: he can know that he is real: that “I am, I exist.”
The “deep whirlpool” is a metaphor for the confusion and uncertainty that people fall into when they entertain radical doubt (the possibility that nothing is real). But this doubt is necessary in order to give science a certain, rational foundation. The Meditator finds this foundation in the very fact that he exists. He knows that he’s thinking; he cannot possibly doubt his own existence. This argument is more commonly quoted in the phrasing Descartes used in his other writing: “I think, therefore I am.”
But what kind of thing is the Meditator? He used to think of himself as a human being with a body and a soul. Yet he has decided to assume that an evil demon is tricking him, so he can’t accept that his body really exists. He also can’t accept some of his assumptions about the soul—like that it’s capable of movement or perception. But he must accept that his soul is thinking. So all the Meditator can know for certain is that he’s “a thinking thing.” To be more specific, he is “a thing that doubts, understands, affirms, denies, is willing, is unwilling, and also imagines and has sensory perceptions.”
Now that he has cleared away all of his previous beliefs, the Meditator starts building them back up, starting from the first principle that he definitely exists. Still, his goal is to be completely sure about all of his conclusions, so he continues to systematically doubt them. This is why he isn’t ready to believe in his body yet—he still hasn’t proven the existence of what he sees and feels. Instead, he sticks to the direct logical consequence of his first principle: if he knows that he’s thinking, then not only does he definitely exist, but he’s also definitely the kind of thing that thinks. The same line of reasoning applies to doubt, understanding, affirmation, and so on. This is significant: Descartes defines human beings primarily in terms of the mind, or rationality. This conception of human nature wasn’t entirely original, but it has deeply influenced philosophy for centuries.
The Meditator finds it bizarre that things he perceives by the (untrustworthy) senses seem so much realer than this thinking self that, according to reason, is all he can absolutely know to be real. To explore this intuition, he decides to let his imagination run wild for some time and then use doubt to rein it back in.
The Meditator has already concluded that the imagination is not trustworthy, so this passage signals a shift in tone. Of course, Descartes has included this shift for good reason: even though the Meditator’s thoughts appear to be spontaneous, Descartes has actually spent years carefully planning them out. Namely, the rest of the Second Meditation will use an example to illustrate the difference between rationality and the senses.
The Meditator considers a piece of beeswax: it appears to have a shape, smell, color, and size, but when put next to a fire, it starts to melt, and all of these qualities change. So its essence has nothing to do with these qualities—rather, its essence is simply to be “something extended, flexible, and changeable.”
The beeswax illustrates how the senses deceive us about the true nature of things. Namely, the senses show us the way an object appears at a particular moment in time, but understanding its inner nature requires analyzing it with the intellect. Just as scientists today would define a substance like the wax through its chemical composition—rather than its color, smell, and texture—Descartes defines it by the fact that it can change forms and has a three-dimensional shape (or is “extended”).
Moreover, nobody could imagine or perceive all the specific shapes the wax could take or ways it could change. Rather, it’s only possible to fully understand its essence through reason. So the senses give an “imperfect and confused” impression of the wax’s nature, while reason gives a “clear and distinct” one. Similarly, when the Meditator sees men crossing through a square, he really just sees coats and hats, and then he uses reason to conclude that there are men under them.
Since the wax could be molded into countless different shapes, no amount of information from the senses could ever enable someone to fully understand its essence. This proves that sensory and intellectual perception are two entirely different abilities. (In contrast to modern usage, Descartes calls both perceptions.) The concept of “clear and distinct” perceptions is also absolutely central to Descartes’s philosophy: it implies a kind of understanding so immediate and well-defined that thinkers truly cannot bring themselves to doubt it.
Thus, reason perceives the world in a more perfect way than the senses do. And when the Meditator understands something like the wax, he knows that it’s him doing the understanding, so he once again proves that he exists as a thinking thing. All of his rational perceptions therefore contribute to his knowledge of his own nature, and in fact, through rationality he can achieve more perfect knowledge about his own mind than about anything else.
Descartes has used the wax as a thought experiment to show why true knowledge about the universe must come from rationality, not the senses. In addition to supporting Descartes’s conclusion that humans’ true essence lies in their minds (and not their bodies), this also explains the importance he puts on knowledge and certainty. Specifically, if humans are essentially just thinking minds, then the highest kind of perfection they can reach is perfect knowledge—meaning that their ideas about the world correspond to its external reality. In other words, for Descartes, science and philosophy are the greatest activities humankind is capable of doing.