non sequitur

In Latin, non sequitur means "it does not follow." The phrase was borrowed into English in the 1500s by people who made a formal study of logic. For them it meant a conclusion that does not follow from the statements that lead to it. But we now use non sequitur for any kind of statement that seems to come out of the blue. The Latin verb sequi ("to follow") has actually led the way for a number of English words. A sequel follows the original novel, film, or television show. Someone obsequious follows another about, flattering and fawning. And an action is often followed by its consequence.