ELI5: Explain Like I'm 5

Axiom of countability

Imagine you have a bunch of toys. The axiom of countability helps you understand how many toys you have.

There are different types of toys - some are big, some are small, some are red, some are blue. But the axiom of countability helps you figure out how many different types of toys you have.

It says that if you can count all the different types of toys - no matter how many there are - then you have what's called a countable set.

For example, if you have 5 blue toys and 3 red toys, you have a countable set of 2: blue toys and red toys.

But if you have a mix of many different types of toys, like some are blue, some are red, some are big, some are small, some are soft, some are hard - it might be harder to count them all and you might not have a countable set.

So the axiom of countability helps us understand how to count things and categorize them.