A pro-form's a type of function word or expression that stands in for (expresses the same content as) another word, phrase, clause or sentence where the meaning's recoverable from the context. They're used either to avoid repetitive expressions or in quantification (limiting the variables of a proposition). Pro-forms are divided into several categories, according to which part of speech they substitute: A pronoun substitutes a noun or a noun phrase, with or without a determiner: it, this. A pr… (More on Pro-form)