Pro-form

In linguistics, a pro-form is 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 is recoverable from the context. They are 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 pro-adjective substitutes an adjective or a phrase that functions as an adjective: so as in "It is less so than we had expected."
• A pro-adverb substitutes an adverb or a phrase that functions as an adverb: how or this way.
• A pro-verb substitutes a verb or a verb phrase: do, as in: "I will go to the party if you do".
• A prop-word: one, as in "the blue one"
• A pro-sentence substitutes an entire sentence or subsentence: Yes, or that as in "That is true".

An interrogative pro-form is a pro-form that denotes the (unknown) item in question and may itself fall into any of the above categories.

The rules governing allowable syntactic relations between certain pro-forms (notably personal and reflexive/reciprocal pronouns) and their antecedents have been studied in what is called binding theory.