 Actual facts are facts about how things are. For example, Mary actually wore her white dress to the party. Modal facts, by contrast, are facts about how things could, must, or could not have been. For example, Mary could have worn her red dress; but she couldn’t have worn a dress that is red and green all over at the same time. Modal reasoning is central to human cognition, since it is pervasive both in philosophy and in every-day contexts. It involves investigating and evaluating claims about what is possible, impossible, essential, necessary, and contingent. Some things could have been different than they actually are, other things could not have been. And some things could have more easily been true than other things. Here are some examples of different kinds of modal claims: