Editing Tip: Using 'That' as a Complementizer

Though we often deal with the word that as a relative pronoun, we rarely talk about its other very common use as a complementizer, wherein it acts as a subordinating conjunction to introduce a clause.

Using that as a complementizer is helpful when certain verbs (e.g., shows, says, indicates, proves) are used to introduce a clause instead of a direct or indirect object:

1. He said [that] "The Thin Red Line" is his favorite movie.
2. These results show [that] the mice in the treatment group healed more quickly than the control mice.
3. The plot indicates [that] an increase in viscosity accompanied an increase in the proportion of particles in the slurry.

In the first example, the sentence would still read fine without that, though adding it doesn't hurt. In this case, that indicates that what follows is not a direct quotation, but a paraphrase, which would be helpful for limiting ambiguity if the sentence were heard instead of being read.

In the second example, that helps make the sentence more readable because it marks the beginning of a long clause.

In the third example, that not only introduces a long clause but also removes ambiguity in how the increase could be interpreted. In this case, an increase is the subject of the verb accompanied. However, without that, one could easily read an increase as the direct object of the preceding verb indicates. In doing so, the reader would not expect that a clause will follow, causing confusion once the the presence of a clause becomes evident.

Another possible ambiguity arises when two dependent clauses follow the main clause of the sentence:

• This method assumes that insolation and temperature variations on the array are insignificant and the constant reference voltage is an adequate approximation of the true maximum power point.

In this example, the reader must make an interpretation. Either the second and is joining two dependent clauses that should both follow the verb assumes, or it is joining a new independent clause that is not part of the method's assumptions. If the latter is true, a comma should be added before the coordinating conjunction. If the former is true, no comma is needed, but the sentence would be much easier to follow if that were repeated before the second dependent clause:

• This method assumes that insolation and temperature variations on the array are insignificant and that the constant reference voltage is an adequate approximation of the true maximum power point.

We hope that this post provides some insight into the use of that to introduce clauses within a sentence. If you have questions about when or how to use that, send an email to [email protected]. Best of luck with your writing!