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We've spent a couple of lessons talking about how philosophers reason. Now, it's time to do some actual philosophy.

One of the most important hallmarks of philosophical thought is that you should never take things at face value. You should always be willing to accept that there's more to the world than meets the eye - because whatever truth seems obvious today might turn out to be not so true at all. It's one of the more daunting pursuits in philosophy: pondering what's really real, as opposed to what you think is real, and how you could ever know the difference.

Fortunately, there are some guides who can help you on your journey when you're exploring the nature of reality. And you know who's really helpful here? Leonardo DiCaprio. I mean I guess you could say that a lot of actors can transport you to another reality if they're good enough, but that's not what I mean.

I'm talking about Inception, that movie where Leo plays a thief who steals ideas from people by invading their dreams - a super handy ability if you want to, say, steal corporate secrets from a CEO or military plans from a head of state. But after a while, it becomes hard for some members of Leo's team to tell the difference between one dream and another, or to discern dreams from reality. The whole film is populated with people who live in a dream world, convinced they're living real life. To them, the dream is all there is. It has become their reality. But from the perspective of those outside the dream, who see their sleeping bodies, the reality they're chasing is simply false.

It's a real cool premise for a movie - I haven't ruined it for you, you can still watch it - and the fact is, the same concept has been around for thousands of years. The basic question that Inception asks has vexed philosophers all the way back to the very roots of Western philosophy. Is it possible that my current reality isn't real at all? And before we had Leo DiCaprio to walk us through this question, we had Plato.

(Theme Music)

Around 2400 years ago, Plato wrote his famous book The Republic in which he describes, probably better than anyone before or since, the nature of reality. He does it by telling a story about prisoners who have been chained since birth in a dark cave facing a blank wall. All kinds of people and objects pass behind the prisoners and a fire casts the shadows of those things onto the wall in front of the prisoners. These shadow images are all the prisoners ever see, so they come to understand the shadows as reality.

Now just hold up a minute and imagine if what your view of the world would be like if all you've ever seen are shadows. You wouldn't know that there was anything more. 3D wouldn't even be a concept for you. 

The prisoners spend their whole lives understanding only this shadow reality until one day, one of them escapes from his chains and crawls into the daylight. After spending a lifetime in fire-lit darkness, the man is blinded by the sun at first, but in time he comes to see the things outside the cave are far more real than the shadow images that he once took for reality. They have more substance, they occupy an extra dimension.

Think about how that would feel, to suddenly realize that everything you believed just minutes ago turned out to be merely faint outlines of reality. This what happens to a lot of the characters who inhabit the world of Inception - once they realize there can be multiple layers of reality, they never look at the world around them the same way again. And for many of them the experience becomes intoxicating.

This is also what happens to Plato's escaped prisoner - he goes back into the cave to tell his friends the exciting news about what he's found, but the conversation doesn't go the way he thinks it will. He expects them to be amazed by his discovery. He figures they'll be as eager to join him as he is anxious to get back, but they all think he's crazy. As far as they're concerned, he's babbling about some higher reality that they've never seen or heard of, or have any evidence for. To make matters worse, going back into the fire-lit cave after being in the sunlight temporarily blinds the man again, so from his friends' perspective, his journey into the outside world has actually damaged him because now he can't even see the shadow images that were once his whole world.

Now, you don't have to be Plato or Christopher Nolan to dream this stuff up. In fact,you might have experienced a diluted version of this kind of reality shock for yourself. For example, do you remember your first teddy bear? That bear was, philosophically speaking, your only contact with, and your only way of understanding, the concept of a bear. Then one day, you went to a zoo or a wildlife refuge or a national park, and you saw an actual bear. And suddenly you realized that your previous understanding of "bear" was way off. Bears don't have little button eyes and smiles made of thread, they're not soft, you couldn't hug one. The bear you spent the first years of your life snuggling with was just a shadowy imitation of the reality of bear-ness.

Now check out this somewhat more mature example: maybe you were the first member of your tweeny group of friends to discover the wonders of romantic attraction. You might have felt like your eyes were opened to a whole new world that your pals were still blind to. And when you tried to explain to them what had happened to you and how you felt, they probably thought you were crazy, and the feeling was probably mutual. And this is what our poor protagonist goes through as he re-enters the cave.

So why does Plato tell us this story? It's not just about the little "a-ha" moments when we discover that bears and boys were not what we once thought they were, it's- it's more than that. Plato wants us to see that we, right now, are prisoners in a cave. Everything in our world is actually a mere shadow of a higher reality. Just as the man in the story once mistook shadows for real things, we are currently prisoners in a cave of our own. But rather than mistaking shadows for the material objects of the ordinary world, our mistake is thinking that the material objects of the ordinary world are the most real things. In fact, Plato says, the physical world that we think is the most real is actually a mere shadow of a higher truth.

If this surprises you, think about how many beliefs were once accepted as absolute fact only to later turn out to be completely false: the shape of the Earth, the idea that the Earth was the center of the universe, the belief that heroin and tobacco and lobotomies were good for people. Those so-called facts turned out to be far from the truth. 

So, there's a lot packed into this little story. Plato is urging you to consider that the world is not really as it seems, and making a statement about philosophy. Doing philosophy is hard. Accepting that much of what you've always believed might actually be false can make you uncomfortable. You might feel temporarily blinded. You may learn just enough to know that your old beliefs aren't reliable, but you don't yet know enough to feel comfortable with these new ideas, either.

What's more, your old friends who aren't on this journey with you might think you've lost your mind. Or they might take you for an arrogant, pedantic jerk who thinks they have all the answers.

But philosophy is also awesome, because once you get through the growing pains, you can see things in a new way and you can see through things that used to fool you.

And that brings us to another puzzle. Consider this argument:
-No cat has 2 tails.
-Every cat has one more tail than no cat.
-Therefore, every cat has 3 tails.

Now you're probably thinking, "That's just clearly wrong, that's not much of a puzzle. I mean the two premises sound right enough, but the conclusion is... what?"

This puzzle exploits the strangeness in the language that we use to discuss certain ideas. Specifically, the ideas of nothingness, absence, or emptiness.

In Premise 1, "no cat" refers to an absence of cats. Think about things with two tails, and none of those things you think of are cats because you probably can't even think of anything with two tails.

But in Premise 2, the language tricks us into understanding "no cat" as an existent thing, rather than an absence of a thing. The way it's phrased, "no cat" could conceivably be that elusive creature that has two tails.

So this leads us to the conclusion that if the "no cat" has two tails and every cat has one more tail than it does, then every cat must have three tails, which is just wrong. And it takes a moment to understand the source of our confusion. The conclusion is faulty because it mistakes the absence of something for the presence of something. But it strikes us as plausible on some level, because language has duped us into considering a reality where a creature called "no cat" with two tails is actually a thing.

Figuring out puzzles like this is kind of like flipping a switch. First you're confused and then the cause of the confusion seems obvious. It's just a matter of sorting through what's really real. And Plato thinks philosophy is like that, too.

Going from the darkness into the light is both disorienting and rewarding. It's kind of too bad in this case, though, because a cat with three tails - I'd kind of like to see that. Though, to be honest, I'd mostly just like looking at any cat.

And with that, we wrap up this episode of Crash Course Philosophy. Today we learned about Plato's famous myth of the cave, questioned the relationship between appearance and reality, and talked about the process of philosophical discovery. Next time, we're going to disappear even deeper into the hole of shadow and disbelief, all in the hopes of eventually emerging into the light.

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