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January 19, 2012

That Versus Which




by Tyler Krupa

This week, we address another item on the list of frequent APA Style points that writers find most challenging (on the basis of the article by Onwuegbuzie, Combs, Slate, & Frels, 2010; also see their guest post to our blog): the use of that instead of which.

According to the 6th edition of the APA Publication Manual (p. 83), APA prefers for writers to use the term that for clauses that are essential to the meaning of the sentence. These types of clauses are referred to as restrictive clauses. The term which should be used for clauses that merely add further information to the sentence that is not essential to its meaning. These types of clauses are referred to as nonrestrictive clauses and should be set off with commas.

To help clear up any confusion regarding the proper use of these terms, let’s begin with looking at some examples of that being used correctly:

It is important to include additional predictors of alcohol or other substance use disorders that were present before treatment.

A poor economy can create and stimulate forces that operate at multiple levels of a society to influence those operating within it.

One way to predict who may benefit from posttraumatic stress disorder treatment is to investigate variables that impact naturalistic recovery.

Note that in each example above, the meaning of the sentence is not properly conveyed if the that clause is not included. These clauses are essential to understanding the sentences and therefore are restrictive.

Now for comparison, let’s look at some examples of which being used correctly:

In the Level 2 equations, the r terms represent random effects, which describe provider variation for the intercept and various client effects.

Binge eating disorder symptom counts, which are identified in Figure 2, were used at each time point.

One key difficult child characteristic is hyperactivity/impulsivity, which has been proposed to contribute to the development of oppositional defiant disorder by eliciting negative family functioning.

Note that in these examples, if you remove the which clause from the sentences, the meaning of each sentence is still conveyed. The which clauses are just providing additional information to the reader and therefore are nonrestrictive.

Consistent use of that for restrictive clauses and which for nonrestrictive clauses will help make your writing clear and precise. If you still have questions regarding the proper use of these terms after reviewing the examples above, feel free to leave a comment, which we will reply to as soon as possible.


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