| After a verb of attribution (said, stated, announced, disclosed), the word “that” often can be omitted with no loss of meaning:
He said (that) he was tired. No need for "that." Better to omit.
But if the words that follow “said” (or any verb of attribution) might be mistaken as objects of the verb, omitting “that” might lead the reader down a false trail:
The governor announced his new tax plan would be introduced soon.
Here “that” is needed after "announced. Without it, the reader's first impression is that the plan itself has been put forth. Remember that even momentary confusion provides readers with a handy place to stop — and that's not good. A reader should never have to pause to understand what the writer (or speaker) is trying to convey. If that happens too often (and once may be once too often), a reader stops reading.
Time element: When a time element is linked to the verb of attribution, the conjunction “that” must be used. For example:
The mayor announced June 1 the fund would be exhausted.
The reader needs to know if the time applies to the material that precedes or follows it. Did he make the announcement June 1? (“...announced June 1 that...”) Or did he say the fund then would be exhausted? (“...announced that June 1...”) In either case, the need for “that” should be obvious. The need remains when the time element is not a date but a day of the week (Monday, Tuesday, today, yesterday, etc.).
“Thats” that travel in pairs
Often a sentence with two parallel clauses requires the expression “and that” to introduce the second clause and link it to the antecedent common to both clauses:
The senator said he might run again and, if he did, Myra Henry would be his campaign manager.
A “that” is needed after “and” to make it clear for the reader. Therefore, a “that” must be inserted after “said” because of a rule called parallelism — if you've got one “that” referring to the same antecedent, you need another. The “that” after “said” is required even though none would be required had the sentence ended after “again.”
The senator said he might run again and , if he did, Myra Henry would be his campaign manager.
So, just remember. If you need one “that” for clarity, make sure you put in another “that” in any compound sentence.
To use “that” or not to use “that”?
That is the question.
The decision to use or omit “that” is not always a simple one. Sometimes it's a judgment call. But don't let your desire to lop off unnecessary words lead you into bad judgment.
As a rule of thumb in questionable cases, remember: Using “that” is never really wrong, though it may be unnecessary; omitting “that” in some cases indeed may be wrong.