I recently got an email from a faithful reader up in Noblesville who has a question about the use of that between independent clauses. He didn’t ask in so many words, but that was his question.
Did I lose you there? Let me explain.
Sometimes, we use that between two clauses:
Bob knew that Sheila was married.
She told him that she was.
She did not, however, tell her husband that she was seeing Bob.
In some cases, it is perfectly acceptable to omit the that. In fact, for informal conversation and writing, the omission of that is sometimes preferred to leaving it in.
That, in many instances, is considered an expletive, or a word with no grammatical function in a sentence. (Expletive meaning a swear word is different. Curse words can have grammatical function in sentences, but I would recommend against using them.) When it is used in the expletive sense, one can use it or omit it without creating an error either way.
The tricky part, of course, is that you cannot always omit that because it is not always an expletive.
While a run-down of all the instances wherein that is necessary versus those in which it is an expletive might be helpful to a few, it would require tremendous explanation, and there’s a fairly easy shortcut: if in doubt, leave that in the sentence. You know that your sentence will be correct with that, and it’s possible that the sentence will be incorrect with that, so just leave it in.
On the flip side, one easy way to remember whether that is needed in your sentence is to take it out and see if the sentence makes sense (or as much sense) without it. If removing that doesn’t create any ambiguity, it’s probably not necessary.
If, however, you still would like to know more about specific cases, pick up a copy of Theodore Berstein’s “The Careful Writer”. He discusses the expletive that in detail.