The overuse of any one word can be irritating to readers (not to mention boring). However, elimination is not necessarily the answer. In English, the word "that" has many uses. While the word "that" can sometimes be dropped to improve concision, other times it is critical to the syntax and meaning of a sentence. In addition, even when the word "that" is not necessary, it can sometimes be used to improve clarity and flow. Therefore, it is necessary for the writer to make purposeful stylistic decisions around the use of the word "that" to create clear and grammatically correct sentences.
When that is used as a pronoun or as a demonstrative adjective, it cannot be eliminated.
"That" as a pronoun:
"That" as a demonstrative adjective:
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 that-clauses serve as the direct object of a reporting verb (such as found, reported, posited, argued, claimed, maintained, and hypothesized) to introduce a paraphrase, summary, or quotation.
Key: Yellow, bold = subject; green, underline = verb; blue, italics = object
Rephrasing these example sentences into questions and answers is one way to see that the that-clauses are acting as direct objects.
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).
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
"That" (as well as "who" and "whose") is sometimes used in a restrictive clause. A restrictive clause restricts or defines the meaning of a noun or noun phrase and provides necessary information about the noun in the sentence. It is not separated from the rest of the sentence by commas. Restrictive clauses are more common in writing than nonrestrictive clauses. A restrictive clause is also sometimes referred to as an essential clause or phrase.
Here are a few examples:
When the relative pronoun (that, which, who, whom, whose) functions as the object of the verb in the relative clause, it can be (and usually is) omitted. Although its use here is not strictly wrong, deleting it from the relative clause creates a more concise sentence.
Here are a few examples:
Relative clauses can also be reduced to phrases to create more sentence variety. When reducing a relative clause, it is necessary to delete the relative pronoun and either delete or change the verb.
Here are a few more examples: