Writers, I want you to do an experiment. Open up your latest manuscript, grab a chunk of it (say, 1000 words), and paste it into a new document. Now, do a find/replace for the word “that.” Replace it with something ridiculous like “Snuffleupagus.” Read the passage out loud. If you’re like me, you’ll be amazed and horrified by how many times you’ve used it.
One of the most common mistakes is using “that” when you really need “which.” The former is for restrictive clauses–clauses that provide essential information, without which the sentence would lose its meaning. The latter is for non-restrictive clauses, which provide additional information or nuance but don’t alter the meaning of the sentence. Let’s take a look at the poem “This Is Just to Say” by William Carlos Williams.
I have eaten
that were in
you were probably
they were delicious
and so cold
In the first stanza, the words “that were in the icebox” specify which plums Williams ate. In the second stanza, the clause “which you were probably saving for breakfast” adds information, but it doesn’t help the reader of the note identify the plums with any more accuracy.
Once you’ve corrected any that/which mix-ups, it’s time to see how many instances of “that” can be omitted. While extraneous “thats” aren’t grammatically incorrect, they do clutter your writing, creating obstacles to trip up your readers. The last thing you want is a reader with a stubbed toe.
Example: She said that I was a going to lose.
The sentence can lose the “that” and still make sense: She said I was going to lose.
According to Neal Whitman’s guest post on Grammar Girl, verbs that function well without “that” are called bridge verbs. It’s difficult to pin down a complete list of bridge verbs; in this paper by Sam Featherston examining the nature of bridge verbs, he writes “if a verb is sufficiently frequent it becomes more transparent to movement.” In other words, common verbs, such as “say,” “think,” “tell,” and “claim,” start to become invisible the more we use them. They transport the reader seamlessly from point A to point B in your writing. This is why “say” is often the best choice for dialogue tags; it’s so common that it doesn’t interfere with your characters’ speech. (See this post for more tips on writing dialogue.)
Like so much about English grammar, it’s difficult to outline a rule that’s true 100% of the time. There are always exceptions. Beyond the that/which rule, everything else is up to the writer. Consider ease of reading, potential ambiguity, and elegance of syntax. Pay attention to the rhythm of your writing. If you’re unsure, read the sentence out loud with and without the “that” and choose the one that sounds the best.