Normal modal logic

Normal modal logic is a type of logic used to reason about things that can be impossible, possible, or necessary. To explain it simply, normal modal logic is like a set of rules that help us think about things in different ways and decide if they are possible or not. For example, if someone said "It is impossible for unicorns to exist", then we could use normal modal logic to say that this is not necessarily true, because it is possible that unicorns exist.