(My essay below appeared earlier today as a guest post for the Content Rules blog.)
I’ve been thinking about that. T-h-a-t. A handier word you’ll never find. Yet English speakers often omit it. That is left out. Suppressed, grammarians say. Implied.
Suppressing that doesn’t necessarily get you in trouble. Sometimes you can safely omit that when it follows a noun. Take shoes. Few misunderstand when you say the shoes you’re wearing instead of the shoes that you’re wearing.
Still, even following nouns, consider keeping your thats out in the open, especially if you write for those wonder workers we call translators or for people who struggle with English. Our language poses enough challenges when all the words are visible.
When it comes to verbs, though, don’t let that go without saying. Whether or not you write for translation, suppressing that creates what Bryan A. Garner calls miscues. He might well have said “missing cues.” Consider these examples:
- Verify the software has been updated.
- Ensure your valuables are locked up.
- The manager doubted the new hire would have any trouble learning the CMS.
Did you notice the missing cues? The word that is missing after each verb. Each time you run across this type of sentence, your mind mistakes the noun for the verb’s direct object. You stop, back up, reread. See what I mean as you scan these snippets:
- Verify the software … [Verify what? The software. Sounds reasonable.]
- Ensure your valuables … [I should ensure my valuables? Shouldn’t I insure them?]
- The manager doubted the new hire … [Then why didn’t the manager hire someone trustworthy?]
Only after your eyes have moved past the noun—software, valuables, new hire—do you realize that you’ve been misled. You do a mental jig-jog: go back, insert that, and continue. Now you get the sentence’s meaning:
- Verify [that] the software has been updated.
- Ensure [that] your valuables are locked up.
- The manager doubted [that] the new hire would have any trouble learning the CMS.
If your mind were a grammarian, it would be shouting, Aha! The noun tricked me. It isn’t the direct object. The direct object is a bunch of words—a whole clause with an implied subordinating conjunction, a missing that. How’s a reader supposed to know that a clause is coming without some kind of cue? Where was my cue? Where was my that?
When you write, don’t leave your readers cueless. End suppression! Release your innerthats. I believe you … I mean, I believe that you and your readers will feel better when you do.
 Garner’s Modern American Usage, 3rd ed., 2009, p. 808.