Yes and no, or word pairs with a similar word, are expressions of the affirmative and the negative, respectively, in several languages including English. Some languages make a distinction between answers to affirmative versus negative questions; thus they may have three-form or four-form systems instead. English originally used a four-form system up to and including Early Middle English but Modern English has reduced this to a two-form system consisting of just 'yes' and 'no'. It exists in many facets of communication, such as: eye blink communication, head movements, Morse Code, and sign language. Some languages, such as Latin, do not have yes-no word systems.
