Modal logic is a kind of logic that helps us understand things that are possible, impossible, necessary, or not necessary. It uses symbols like ◉ (which means it is possible), ~~◉ (which means it is not possible), [[◉]] (which means it is necessary), and ~~[[◉]] (which means it is not necessary). We use modal logic to help us think about things that might be true or false. It can also help us think about things that are impossible or necessary.