I’ve known many copyeditors who fixate on that as a word that serves little purpose and can be deleted without much thought about the sentence that surrounds it. It is often optional, but that doesn’t mean it never provides clarity.
E.B. White suggested that we “omit needless words,” which is excellent advice that writers and editors have applied overzealously for decades. A word is not needless because the sentence can theoretically stand up without it. A word is needless when it adds nothing: not context, not direction, not nuance, not rhythm. I’ve never met a piece of writing that couldn’t be shortened, but shorter is not alway better.
Strunk and White’s “omit needless words” entry includes this advice:
Vigorous writing is concise. A sentence should contain no unnecessary words, a paragraph no unnecessary sentences, for the same reason that a drawing should have no unnecessary lines and a machine no unnecessary parts.
I know copyeditors who would delete the that (did you notice it?) and pat themselves on the back for making the paragraph more concise.
Consider also the first sentences of Hemingway's The Sun Also Rises:
Robert Cohn was once middleweight boxing champion of Princeton. Do not think that I am very much impressed by that as a boxing title, but it meant a lot to Cohn.
Here is Emily Nussbaum writing about David Letterman in The New Yorker:
His manner suggested that TV could puncture the culture, rather than prop it up.
We could delete all these thats with little harm. But if we’re to do no harm, we ought to think twice and leave them in. They offer a subtle signal to the reader, a helping hand concerning the subject and action and what might be coming next. We read from left to right for the most part, and signals along with way make the writer’s thoughts easier to digest.
There are more explicit cases where leaving out that creates confusion.
He chose the more expensive shop because he believed the mechanic, who came recommended, would do a good job.
Without that, we first think the decision was based on belief that the mechanic was being truthful, and later understand that it was based on belief that mechanic was capable.
He chose the more expensive shop because he believed that the mechanic, who came recommended, would do a good job.
I’ve encountered the anti-that crowd on many newspaper copy desks, but don’t blame the Associated Press Stylebook, whose entry suggests there are no clear rules. The Stylebook entry on that concludes with some broadly applicable advice:
When in doubt, include that. Omission can hurt. Inclusion never does.