What is the problem of induction?

0:00 Welcome to Philosophy is not boring by Kidopoly.com. I'm Mira! And I'm Finn. If you haven't already, tap follow wherever you're listening so you never miss an episode.

0:12 Okay, I am so ready. What are we thinking about today?

0:17 Well, I have a very simple question for you, Finn. How do you know the sun will rise tomorrow?

0:24 Uh because it always does? It rose today, it rose yesterday, it rose the day before that.

0:31 Exactly! But what if I told you that all those past sunrises don't actually prove anything about tomorrow? Wait, what? Yes they do! That's how we know. That's what almost everyone thinks. But what if your expectation that the sun will come up isn't based on facts or pure logic at all? What if it's just a habit?

0:54 Think about how our whole lives are built on expecting things to repeat. You expect the floor to hold you up when you get out of bed.

1:02 Yeah, because it's a solid floor. If I step down and fall through, I'm going back to sleep.

1:08 And you expect your favourite breakfast cereal to taste like cereal, not like spicy mustard. Obviously. That would be terrible. But how do we actually know the future will be exactly like the past? Because that's just how the world works, Mira. Well, back in 1748, a brilliant Scottish philosopher named David Hume decided to really chew on that idea.

1:32 He published a famous book called An Inquiry Concerning Human Understanding. What was he trying to understand? He noticed a massive problem with how human beings think. He pointed out that we make all our predictions about the unknown future based entirely on what we've seen in the past.

1:51 Right. Like, I know my dog will bark at the mail carrier tomorrow, because he has barked at the mail carrier every single day of his life. Exactly.

2:00 That's called an inductive inference. You take specific observations from the past and you make a general rule about the future.

2:08 And that rule is true. My dog will definitely bark.

2:11 But Hume asked, is it logically guaranteed? What makes you so absolutely sure? Can you logically prove he will bark tomorrow? Let's look at an even bigger example. Imagine you're eating a fresh, crunchy apple. It nourishes you and gives you energy. Why? Because it's an apple. They grow on trees and they are food.

2:34 But how do you know the next apple you eat won't mysteriously turn into a block of wood or just float up to the ceiling?

2:43 Because of science, Mira. Biology makes it food, and gravity keeps it from floating. We've studied how it works.

2:50 Okay, but your science is all based on past apples. How do you know the laws of nature will work tomorrow exactly the same way they work today? Because well, because they always have. There's a famous story philosophers use to explain why this is a trap. Imagine a chicken on a farm. Every single morning, the farmer walks out to the coop.

3:13 And brings the chicken delicious seeds and corn. Exactly. Day one, food. Day 50, food, day 100, food. The chicken, being a very logical thinker, makes a firm rule. Every time I hear the farmer's footsteps, I am getting fed. The chicken has a lot of data. That's good science. Right, but then, one morning, the farmer walks out.

3:38 And instead of food, he brings a wooden crate, packs the chicken up, and drives it to a completely different farm. Wait! The chicken's rule was totally wrong. Exactly! The chicken used perfect inductive reasoning. It used solid past evidence to predict the future. But Hume pointed out that no amount of past evidence logically guarantees the future.

4:01 But wait, humans are way smarter than chickens. We know why the sun rises. We know the earth spins in space. We do, but why do you believe the earth will keep spinning tomorrow? Because it kept spinning yesterday and the day before. Stop right there! Do you hear what you just did? What? I just said it always has worked, so it will keep working.

4:26 You just use the past to prove that the past is a reliable guide to the future. It's like saying, I know my magic eight ball tells the truth, because yesterday the magic eight ball told me it tells the truth. You're stuck in a loop.

4:40 Oh wow! I'm saying the future will be like the past. Because in the past, the future was like the past.

4:48 Yes, that is the trap. David Hume brilliantly pointed out that there is absolutely no pure logical reason to assume the future will resemble the past. Even the laws of physics could technically change tomorrow.

5:01 That is kind of terrifying. If we can't logically prove anything about tomorrow, are we just guessing? Does science mean nothing?

5:09 Not at all. This is famously called the problem of induction, and nobody has perfectly solved it since 1748. But here is the reassuring half. Hume didn't say we should stop predicting things.

5:23 He didn't?

5:24 Nope. He actually said that this expectation is exactly how human minds are built to work. We notice a pattern, we expect it to happen again, and we keep checking. Hume said this habit is totally necessary for survival. So it's not perfect logic, it's just a really good habit. Yes, and a much later philosopher named Karl Popper added to this.

5:48 He said science isn't about proving things perfectly true forever anyway. It's about making our absolute best guess based on patterns and then trying to prove it false.

5:58 So if we can't prove it false, we just say, well, it's the best rule we have right now. Exactly.

6:05 We haven't seen a day where the sun didn't rise yet, so we trust our habit. But what does this problem of induction mean for your real life?

6:15 Yeah, I'm not exactly a scientist measuring the sun.

6:18 Well, think about the last time you were in an argument with a friend or a sibling, and you yelled, but you always do that.

6:27 Oh yeah. Like if my friend always interrupts my stories. I get super annoyed because I expect them to do it before they even open their mouth.

6:37 Right, you're making an induction. You took past experiences and turned them into a solid, unbreakable rule about the future.

6:45 Because they interrupted me three times yesterday.

6:48 But Hume reminds us that the past doesn't guarantee the future. Just because your friend interrupted you yesterday doesn't logically mean they will today. People aren't planets. People can learn and they can change.

7:02 Oh wow. That's actually a really nice way to think about it. If you remember the problem of induction, it keeps your mind open. You don't have to be totally trapped by what happened in the past.

7:15 Exactly. You give people space to surprise you. And speaking of surprises, Hume didn't let this massive, brain-breaking puzzle ruin his life.

7:25 He didn't? Because if I figured out that logic can't guarantee tomorrow, I'd probably just hide under my blankets and panic.

7:33 A lot of people might. But Hume was famous for being a really cheerful guy. When he got what he called philosophical melancholy from thinking too hard, he had a great trick. What did he do? He wrote that he would just leave his desk, go dine with his friends, be merry, and play a game of batgammon. Batgammon?

7:54 Like the board game with the checkers and the dice. Yep. He said after a few hours of playing games and laughing with his friends, all those deep, stressful thoughts seemed completely ridiculous, and he could just enjoy being a regular human being.

8:10 I love that so much. He completely broke philosophy and then just went to play a board game.

8:16 Alright, Finn, time for the quiz. Are you ready? Okay, I'm ready. Okay, first question. Who was the cheerful Scottish philosopher we talked about today? Next one, this is tricky. What year did he write about this problem in his famous Inquiry? Question 3. What is the name of the puzzle about predicting the future from the past?

8:48 Alright, here's number four. What board game did Hume play to relax his brain? Last question. Instead of pure logic, what did Hume say makes us expect the sun to rise? Great job! Let's go through the answers. The answer to question one is David Hume. For question two, he published it in 1748. Number three, the answer is the problem of induction.

9:23 Question four, he played Batgammon. And the final answer is Habit.

9:29 You know, I'm going to look at the sunrise completely differently tomorrow. It's not just a boring guarantee anymore, it's kind of a nice surprise every single time. I love that.

9:40 We don't have perfect logical certainty about tomorrow. And that's exactly what keeps the world interesting.

9:46 If this episode didn't make your brain hurt too much, please leave us a five-star review. Just scroll down and tap the stars.

9:54 And please follow this show wherever you're listening, so new episodes turn up on their own. Oh, and we have sister shows too. History and science is not boring, and maths is not boring. Go give those a listen and a follow as well.

10:09 Want your name on the show? Send us an email at hello at kidopoly.com.

10:14 See you next time on Philosophy is not boring. Bye, everyone.