It’s easy to take negation for granted, and not give it a second thought. Either it will rain or it won’t rain. But definitely it won’t rain and not rain at the same time and in the same place. Looking at it like that, you can take your pick. Raining and not raining are on a par, like heads and tails. You can have one or the other, but not both.

So it may seem at first glance. But on closer inspection, the reality is different. The world is a positive, not a negative place, and human ways of organising our thoughts about the world are mainly positive too. We directly observe only positive facts, like this coin is showing heads, or it is raining. We have to derive the negation of a positive fact from the absence of the positive fact. The fact that this coin is showing heads implies that it is not showing tails, and the fact that it is sunny implies, everything else being equal, that it is not raining at the same place and the same time.