The word "that" has a few different functions in English, which can lead to confusion because some instances of "that" are more optional than others in academic writing.

One important use of "that" is for embedding (inserting) a certain type of dependent clause called a noun clause into an independent clause. Frequently, such clauses serve as the direct object of a reporting verb (e.g., found, reported, posited, argued, claimed, maintained, and hypothesized) to introduce a paraphrase, summary, or quotation.

Also see our webpage for other Uses of "That."

 

Key: Yellow, bold = subject; green, underline = verb; blue, italics = object

 

For example,

• Smith (2015) reported that more research was necessary.
  • Smith (2015) = subject
  • reported = verb
  • that more research was necessary = dependent clause, direct object of the verb reported
• The authors hypothesized that there would be significant results.
  • The authors = subject
  • hypothesized = verb
  • that there would be significant results = dependent clause, direct object of the verb hypothesized
• Jones (2014) asserted that confidentiality was maintained throughout the study.
  • Jones (2014) = subject
  • asserted = verb
  • that confidentiality was maintained throughout the study = dependent clause, direct object of the verb asserted
• Rephrasing these sentences into questions and answers is one way to see that the "that"-clauses are acting as direct objects.
  • What did Smith (2015) report?
    • Answer: that more research was necessary
  • What did the authors hypothesize?
    • Answer: that there would be significant results
  • What did Jones (2014) assert?
    • Answer: that confidentiality was maintained throughout the study

In formal written English, for clarity, most academic writers choose to keep "that" when it introduces a noun clause (Caplan, 2012). Leaving out "that" can cause the reader to misread (at first anyway) the subject of the dependent clause as being the object of the reporting verb (Jamieson, 2012).

• For example, if readers see the sentence, "Smith (2015) reported more research was necessary" (without "that"), they may understand “more research” as the thing Smith reported and then have to backtrack and reread upon seeing “was necessary.”
• Any structure that leads to misinterpretation, even temporarily, can be an unwanted distraction from the writer’s message.
• In spoken English, however, "that" may be dropped in such sentences. (Intonation patterns—rising and falling pitch—give the listener clues that may not be present in writing.)

 

References

Caplan, N. (2012). Grammar choices for graduate and professional writers. University of Michigan Press.

Jamieson, P. (2012). Use of that. http://www.proofreadnow.com/blog/bid/89915/Use-of-That