Descartes and radical skepticism

I always know when I’m about to get sick because I have very vivid dreams. They’re often frighteningly real, and I’ll wake up and not be sure of whether I’m still dreaming or not. Once or twice I’ve even had sleep paralysis, and I’ve “woken up”, only to find that I can’t move, and that strange things are happening inside my room. I still remember one night where I dreamt that I was trapped inside my bed, and that it was slowly heating up. I had a nightmare that I’d be baked alive, and I was really shaken by it the morning after.

If you’re like me, you probably would do your best to forget a nightmare like that. However, if you’re more a philosopher, it’d make you think. You might start thinking about how vivid that seemed, and how you were unable to tell it from reality. Then, a realization: how do you know that you’re not dreaming right now? Isn’t it possible that this is just a long-lasting dream, one which you’ll wake up from eventually?

This is what Rene Descartes, 17th century French philosopher, started with. Except he took it in an interesting direction. From this point, Descartes asked what our basis is for knowledge in the first place. Remember, at this point we’ve covered two broad categories of knowledge: Aristotle’s syllogisms, which are a form of deduction, and Bacon’s reasoning from careful observations, which is a form of induction. Now Bacon knew that induction could be a difficult process, and Aristotle was wary of improper syllogisms, but both thought the foundation of these processes were sound. Descartes disagreed.

Remembering how realistic his dreams were, Descartes proposed a thought experiment. What if a demon (or, in Descartes’s words, an “evil genius”), made it his life’s mission to mess with Descartes? First of all, he’d obviously start with hallucinations. He’d make Descartes constantly see things as he did in dreams. Descartes would see people and things that aren’t there, and never be sure if what was in front of his face was really in front of his face.

This would knock out any hope we had of performing Bacon’s new method of science. If we can’t rely on what we observe, then we’d have no hope of using what we observe to form conclusions about the world. But Descartes isn’t finished yet. He asks about what would happen if this demon made him perform deduction wrong as well. For instance, what if every time that Descartes tries to add 3 and 5, the demon interferes with his thoughts, and makes Descartes answer 9?

Someone like Aristotle would, of course, say this is preposterous. Everyone has had vivid dreams, but the great Aristotle would never perform simple math incorrectly, no matter how powerful the demon. But Descartes was a great mathematician, far more accomplished than Aristotle, and Descartes admitted that he made careless math errors. If Descartes could make a careless arithmetic error when he was tired, then it’s possible he could have been making errors all the time, in the same way he could be constantly dreaming.

So the demon could destroy Descartes’s ability to perform deduction as well. Now Descartes is in trouble. He couldn’t rely on his ability to reason, because the demon could mess with that. He couldn’t rely on his ability to observe and assume, because the demon could mess with that. We could even say (although Descartes didn’t) that he couldn’t assume that demons don’t actually exist, because that would rely on logic and our experience, both things that a demon could attack. Descartes, for his part, is saved only by his faith in God, and his belief that God is too good to allow something like this to happen. But still, this is a lonely and frightening path that Descartes has walked down.

Then Descartes has a revelation, likely the most famous one in all of philosophy. Cogito ergo sum. I think, therefore I am. Every time he thinks that he exists, he has to exist. After all, even if a demon has fooled him about everything else, the demon has to fool him. That is, there has to be someone for the demon to trick, and therefore, Descartes knows he exists.

Descartes goes on after this, but I want to stop with his thought process here. The question is what we can learn from Descartes. This is an undoubtedly an impressive piece of philosophy, and there’s a reason why Descartes is so famous. But it seems a bit pointless to discuss if there’s nothing to learn from it, and we can only admire it without ever hoping to emulate it.

Well, the good news, for you and for my essay series, is that there is something to learn from it. I want to focus on Descartes’s radical skepticism. Descartes slowly and systematically digs out all of his knowledge, including the roots. While there were skeptics before Descartes, nobody before Descartes had dared to question their knowledge to such an extent.

It is rare in this world that is necessary to question knowledge like this. After all, normally we can assume that what we’re certain of is true. It might not be. It’s possible we’re living in the Matrix, and the walls that seem so solid to us are really just cleverly constructed pieces of computer code. Still, no matter the true nature of the walls in whatever room you’re in, I would not recommend attempting to walk through them. You’re liable to give yourself quite a headache.

However, there are occasions in which it is necessary to question our fundamental assumptions. In the words of historian of science and philosopher Thomas Kuhn, these are paradigm shifts. Paradigms aren’t just opinions, facts, or theories, but ways of looking at the world and structuring our thoughts. A paradigm shift, therefore, is an entirely new way of looking at a field, with new concepts, terms, and models.

Kuhn’s most famous example of a paradigm shift was the shift from the Earth being the center of the Solar System to the Sun being the center of the Solar System. By the 16th century, an elaborate system of theories had been built up to support the Earth being the center of the Solar System, a paradigm known as the Ptolemaic system. Named after 1st century Greco-Egyptian scientist Ptolemy, it proposed that all the stars and planets revolved around the Earth. This system seemed good, but astronomers noticed that it often seemed that planets and stars would stop in their rotation, or even move in reverse. Their explanation was that occasionally planets and stars would rotate in tiny orbits within big orbits, which they called epicycles.

These epicycles were complicated, and had to be constantly modified to support new observations. To our mind, they seem ridiculous. However, no astronomer was willing to question the fundamental assumption that the Earth was the center of the Solar System, so no better system was developed. It fell to two men to question this fundamental assumption: Copernicus and Galileo.

Copernicus was the first. He proposed that the Earth revolved around the Sun, rather than vice versa. However, he didn’t go far enough. Copernicus still believed in epicycles and the system of physics that underpinned it, Aristotelian physics (which we’ve discussed the problems of before). These ideas supported geocentrism (Earth-centering), not heliocentrism (sun-centering). His intuition was correct, but he didn’t have the tools to defend it. So his idea was discarded by his fellow astronomers.

Galileo, on the other hand, was willing to dig up his knowledge by the roots, much like Descartes did about 40 years after. Galileo asked the unthinkable: what if astronomers weren’t just wrong about the structure of the Solar System, but about physics itself? Specifically, Galileo proposed that Aristotle’s old idea that an object in motion will naturally come to a halt was false. Instead, Galileo said that an object in motion will stay in motion, unless acted upon by an outside force. Therefore, epicycles would never make sense. No planet would ever just stop, or move in reverse. It could appear to move in reverse, but only from the perspective of Earth, because Earth itself was constantly moving and rotating.

This wasn’t the end of the Copernican Revolution, but it was the start. The math of Kepler, the physics of Newton, and, finally, the reluctant acceptance of the Catholic Church were all necessary components before the Revolution could conclude. Eventually, though, the idea that Earth was the center of the Solar System seemed ridiculous, and a new paradigm was firmly established, with accompanying terms, equations, and models.

It’s important to note exactly how radical this revolution was. Each of these scientists had to go against hundreds of years of science and religion in order to make their claims. They had to question what they had supposedly seen with their own eyes, like planets going backwards in their orbit, as well as what had supposedly been proven by logic and mathematics. Much like Descartes, there had to have been periods where they felt alone, unsure of what they could trust and what they could claim to actually know.

There will be very few times in your life when it is necessary for you to question the foundations of your knowledge. As I said before, most of the time your assumptions about what is true will serve you fine. But there will come a time when some system of knowledge seems questionable to you. Perhaps you will find yourself doubting a superstition of your mom, a theory of your professor, or even your own basic assumptions about the reality of your world. When that time comes, I encourage you to be bold, and to not hesitate to question. Pursue your line of questioning to its conclusion, wherever it may lead you, and do not be afraid to clear out everything and start anew.

For my next essay, I’ll continue my discussions of skepticism, with the famous Scottish skeptic David Hume. We’ll explore causation, and what it means when we say something “causes” something else. I’d tell you to be excited, but I’ll skip that for now. After all, whether you choose to be excited or not excited, you should come to that conclusion by yourself. I’m just here to light the way.

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