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Grammar Tip: The Ambiguous Antecedent

Have you ever found yourself re-reading a sentence because you came across a word such as "it" or "them" and could not tell which of two things it referred to?

You probably do not want your readers to puzzle over the same thing. This grammar tip describes a common error in the use of pronouns to help you avoid this problem.

A pronoun (e.g., you, ours, she, this, whom, which, himself) takes the place of a noun or another pronoun, often to avoid repetition. The noun, pronoun, or clause that a pronoun refers to, called an antecedent, usually appears earlier in the sentence, although it can also appear later.

A pronoun should refer to one specific antecedent. An ambiguous pronoun antecedent occurs when a pronoun has two or more possible antecedents.


In the following example, does the pronoun it refer to the first study or to the second study?

The second study was designed to enrol 2000 more participants than the first study. It tested three dose levels of the study drug.

The corrections show how the sentence can be written more clearly. One way is to rearrange it and delete the pronoun, as shown in the first correction. In the second correction, shortening the sentence and deleting the pronoun produces the same result.

Correction 1
The second study, which tested three dose levels of the study drug, was designed to enrol 2000 more participants than the first study.

Correction 2
The second study, designed to enrol 2000 more participants than the first study, tested three dose levels of the study drug.

In the next example, the pronoun them sets up an amusing possibility: McFarlane et al. either presented their study results or presented the previous researchers!

The pronoun those is not ambiguous because it refers to only one antecedent (results).

McFarlane et al. compared their study results with those of previous researchers and presented them at the conference.

At the conference, McFarlane et al. presented their study results, which they had compared with those of previous researchers.

Quick Tips: The Ambiguous Antecedent

Speedy pencil: quick grammar tips
  1. Re-read your document, paying close attention to each pronoun to ensure that it refers to only one antecedent.
  2. To correct an ambiguous antecedent, remove the pronoun, shorten the sentence, or rearrange sentence elements. You may need to do all three.


The Chicago Manual of Style. 15th ed. Chicago, IL: The University of Chicago Press; 2003.

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