Ameka classifies these two words in different ways according to context. When used as back-channel items, he classifies them as interjections; but when they are used as the responses to a yes-no question, he classifies them as formulaic words. The distinction between an interjection and a formula is, in Ameka's view, that the former does not have an addressee (although it may be directed at a person), whereas the latter does. The yes or no in response to the question is addressed at the interrogator, whereas yes or no used as a back-channel item is a feedback usage, an utterance that is said to oneself. However, Sorjonen criticizes this analysis as lacking empirical work on the other usages of these words, in addition to interjections and feedback uses.
Bloomfield and Hockett classify the words, when used to answer yes-no questions, as special completive interjections. They classify sentences comprising solely one of these two words as minor sentences.