How many types of people are there in the world?

There are three types of people in the world: Those who can count; and those who can't.

There are 10 types of people in the world: Those who know binary; and those who don't.

I always wanted to msg Today Today on triplej and suggest for their 'Two Types of People' segment: Two Types f People: Those who ring up the radio; and those who don't. Ahhahahaaha. How witty I was. Humph.

Anyway, this 'type' of joke has got me thinking about something my dad used to say. And what he used to say was that there is only a finite number of jokes in existence (I think he said five), and that any joke anyone ever invented would always fit into one of these categories. It's a strange thought. A finite number of types of jokes. I don't know what the categories are, but has anyone else ever heard of such a theory? Or do you have any suggestions for categories?

The memory is such a distant one. Perhaps my dad was making a joke in proposing such a theory, and I was just too young to 'get it'...