We don't know whether it's heads or tails, but we can start to describe the chances of it being heads or tails. And we'll talk about different ways of describing that. So one way to think about it, and this is the way that probability tends to be introduced in textbooks, is you say, well look, how many different equally likely possibilities are there? So how many equally likely possibilities? So number of equally likely possibilities. And of the number of equally likely possibilities, I care about the number that contain my event right here. So the number of possibilities that meet my constraint.