Communication is difficult enough under the best of circumstances, so we need to do everything possible to ensure that our writing is as clear and unambiguous as possible.

One extremely common mistake that hampers clarity and can result in ambiguity is failing to have clear antecedents for pronouns, and the worst offender is the broad “which” (sometimes referred to as the implied or vague “which”).

What Is an Antecedent Anyway, You Ask?

A pronoun’s antecedent is the noun or other pronoun it is replacing or to which it refers. In the sentence “Emily fell off her horse,” the antecedent for “her” is “Emily.” The prefix “ante” means “before,” so think of an antecedent as the word that comes “before” the pronoun (though occasionally it comes after, as in the sentence “In her latest blog post, the author focuses on strategies for staying on top of one’s horse”).

Pronouns Need Clear Antecedents

Often we use “which” to launch a relative clause (so called because the pronoun relates to a noun or other pronoun that has already been stated—its antecedent). Relative clauses are adjective clauses: they modify the noun or pronoun to which the relative pronoun (in this case, “which”) refers (or relates). (Other relative pronouns are “that,” “who,” “whom,” “whose,” and occasionally “when” and “where,” which are called “relative adverbs”).

The boldface text in this example sentence is a relative clause:

Three recent experiments on the effects of sleep deprivation reveal a clear connection between sleep quality and cognitive functions, which decline in direct proportion to sleep deficit.

In this sentence, the pronoun “which” clearly refers to the antecedent “functions.” We can test it to be sure by replacing “which” with “functions” and asking ourselves if the clause is still accurate; in this case, we are, indeed, being true to the intent of the original sentence if we say “functions decline in direct proportion to sleep deficit.”

[Note: Its antecedent determines whether “which” is singular or plural; in this case, since the antecedent is plural (“functions”), the verb must be plural (“decline”), not singular (“declines”).]

Houston, We Have a Problem

But what often happens is that “which” has no antecedent at all or very broadly refers to the entire idea in the main clause. Consider this example:

*Three recent experiments on the effects of sleep deprivation reveal a clear connection between sleep quality and cognitive functions, which led researchers to promote better sleep health.

In this sentence, the relative pronoun “which” does not have a clear antecedent.  That is, there is not a single noun in the main clause for “which” to refer to specifically—not “experiments,” not “effects,” not “deprivation,” not “connection,” not “quality,” and not “functions.”

We might reasonably say that “experiments led researchers to promote better sleep health,” but that sentence does not precisely express the intended meaning: It was the specific “results” of those experiments, not the experiments themselves, that led researchers to promote better sleep. But the noun “results” (or one of its synonyms) is nowhere to be found to provide a specific reference for “which.”

Any time “which” refers not to a single word but to an entire clause, we have a broad “which.” This construction is frowned upon because it results in unnecessary vagueness. At best, the sentence is not as clear as it could be, and at worst it could be downright ambiguous.

How Not to Revise the Broad “Which”

Now that we can recognize a sentence with a broad “which,” we need to know how to improve it.

First, resist the temptation to reduce the clause to a participial phrase (in bold below); if there is no antecedent for “which” to point to, then there is also no noun for the participle to modify, and the revised sentence would contain a dangling modifier:

*Three recent experiments on the effects of sleep deprivation reveal a clear connection between sleep quality and cognitive functions, leading researchers to promote better sleep health.

If we ask ourselves, “Who or what was ‘leading researchers to promote better sleep health,’ the answer is not “functions” or, for that matter, any other noun in this sentence. The participial phrase is dangling because it has no noun to modify.

Better Suggestions

Instead, here are three effective approaches to eliminating the broad “which”:

1. Add a noun phrase that provides the missing antecedent for “which.” This approach works but is wordier than some other options:
   

   Three recent experiments on the effects of sleep deprivation reveal a clear connection between sleep quality and cognitive functions, a result that led researchers to promote better sleep health.

   [Note: We changed “which” to “that” (both of which are relative pronouns in this construction) because the clause is essential. Read our article on which vs. that to learn why that is the better choice here.]

2. Change the relative clause to a verb phrase. Now the sentence, whose subject is “experiments,” has compound verbs—”reveal” and “have led”—and the vague “which” is gone.
   

   Three recent experiments on the effects of sleep deprivation reveal a clear connection between sleep quality and cognitive functions and have led researchers to promote better sleep health. 

3. Use a coordinating conjunction and change the dependent “which” clause into an independent clause:
   

   Three recent experiments on the effects of sleep deprivation reveal a clear connection between sleep quality and cognitive functions, so researchers have begun promoting better sleep health. 

   *Indicates an ungrammatical sentence.