[2] There are also languages such as English, German and Swedish that only allow pro-drop within very strict stylistic conditions.
But they can also be classified as a distinct part of speech, given that (other) interjections have meanings of their own and are often described as expressions of feelings or emotions.
The Portuguese word sim (yes) gives a good example: In some languages, such as English, yes rebuts a negative question, whereas no affirms it.
The English words "yes" and "no" were originally only used to respond to negative questions, while "yea" and "nay" were the proper responses to affirmative questions; this distinction was lost at some time in Early Modern English[citation needed].
The prosentential theory of truth developed by Dorothy Grover,[4] Nuel Belnap, and Joseph Camp, and defended more recently by Robert Brandom, holds that sentences like "p" is true and It is true that p should not be understood as ascribing properties to the sentence "p", but as a pro-sentence whose content is the same as that of "p." Brandom calls " .