Blackstone's formulation

Okay, so imagine you have a big bowl of candy. You really want to eat all of it, but your mom says you can only have one piece. You start to cry because you want more candy.

But then your mom says, "Okay, how about this? You can have one piece of candy now, but if you don't cry or throw a tantrum for the rest of the day, you can have another piece before bed."

That is kind of like what Blackstone's formulation is. It is a way of saying that punishment should only happen if someone breaks a rule or law. You can't just punish someone because you think they might break a rule in the future.

So, in our candy example, your mom is basically saying that you can only be punished for breaking a rule (crying or throwing a tantrum), not for something you might do later on (ask for more candy).

Blackstone's formulation is important in the legal system because it helps to ensure that people are treated fairly and not punished for things they haven't actually done yet.