In grammar, an antecedent is one or more words that identifies a pronoun or other pro-form. For example, in the sentence "John arrived late because traffic held him up," the word "John" is the antecedent of the pronoun "him." Pro-forms usually follow their antecedents, but sometimes precede them. In the latter case, the more accurate term would technically be postcedent, although this term is not commonly distinguished from antecedent because the definition of antecedent usually encompasses it. The linguistic term that is closely related to antecedent and pro-form is anaphora. Theories of syntax explore the distinction between antecedents and postcedents in terms of binding.

Almost any syntactic category can serve as the antecedent to a pro-form. The following examples illustrate a range of proforms and their antecedents. The pro-forms are in bold, and their antecedents are underlined:

This list of proforms and the types of antecedents that they take is by no means exhaustive, but rather it is intended to merely deliver an impression of the breadth of expressions that can function as proforms and antecedents. While the stereotypical proform is a pronoun and the stereotypical antecedent a noun or noun phrase, these examples demonstrate that most any syntactic category can in fact serve as an antecedent to a proform, whereby the proforms themselves are a diverse bunch. The last two examples are particularly interesting, because they show that some proforms can even take discontinuous word combinations as antecedents, i.e. the antecedents are not constituents. A particularly frequent type of proform occurs in relative clauses. Many relative clauses contain a relative pronoun, and these relative pronouns have an antecedent. Sentences 'd' and 'h' above contain relative clauses; the proforms when and which are relative proforms.

In some cases, the wording could have an uncertain antecedent, where the antecedent of a pronoun is not clear because two or more prior nouns or phrases could match the count, gender, or logic as a prior reference. In such cases, scholars have recommended to rewrite the sentence structure to be more specific, or repeat the words of the antecedent rather than use only a pronoun phrase, as a technique to resolve the uncertain antecedent.

For example, consider the sentence, "There was a doll inside the box that was made of clay", where the word "that" could refer to either the box or the doll. To make it clear that the doll is what is made of clay, the sentence could be reworded as one of the following: "Inside the box, there was a doll that was made of clay", "Inside the box, there was a doll made of clay", or "There was a girl doll inside the box, and she was made of clay" (or similar wording).

Antecedents may also be unclear when they occur far from the noun or phrase they refer to. Bryan Garner calls these "remote relatives" and gives this example from the New York Times:

"C-130 aircraft packed with radio transmitters flew lazy circles over the Persian Gulf broadcasting messages in Arabic to the Iraqi people that were monitored by reporters near the border."

— Patrick E. Tyler, “War Imminent as Hussein Rejects Ultimatum,” N.Y. Times, 19 Mar. 2003