"Are 'recur' and 'reoccur' both correct, and do they mean the same thing?" A simple question from reader Lloyd, and a good one. But like most grammar and usage questions, the answer isn't quite so simple.
Whenever someone asks me to delineate between two similar words, or two commonly confused words, the most urgent issue always seems to be: Is it an error to use them as synonyms? Must each be designated its separate meaning? Are you in danger of making a mistake if you use them willy-nilly?
It's a knee-jerk reaction. I've been busted making more mistakes than I care to recall. It's no fun. So technical correctness is always my first concern. But for less gun-shy types, more important questions might be: How do you use these words well? What deeper insights are to be had about their subtle or not-so-subtle shades of meaning?
If you worry only about technical correctness, answers are easy to find. In most cases, you just have to check a couple of dictionaries.
Under its listing for "recur," Webster's New World College Dictionary includes this definition "to occur again." Merriam-Webster does the same.
So now all we have to do is look up "reoccur" and see if its definitions overlap. There's just one problem: "Reoccur" isn't in either dictionary.
Here's where you have to know a little about how dictionaries work. Normally, when a word is not in a dictionary, it means it's not sanctioned by that dictionary. In effect, it's not legit. But an important exception to this rule is at work here: prefixes.
Prefixes and other "combining forms" attach to existing words to make terms that, though not in the dictionary, are still valid.
Because "reoccur" isn't in our dictionaries, we have to note that "re" is a prefix and is "occur" a word. That means that "reoccur," despite not having its own dictionary entry, is legitimate. And if you know the meanings of the prefix and the verb, we know "reoccur" means "to occur again," just as "recur" often does.
Voila. You can use both "recur" and "reoccur" in this way.
Yet strong opinions to the contrary exist. "Something that is recurring happens over and over again, possibly at regular intervals," Grammarly advises. "Something that is reoccurring is simply happening again."
That's not true, as we've just seen. Merriam-Webster's Dictionary of English Usage (a usage guide that, contrary to the name, should not be confused with a dictionary) puts it this way: Yes, "recur" does suggest a repetition while "reoccur" emphasizes that something may have happened only once before. But that's a trend, not a rule.
"'Reoccur' and 'reoccurrence' are the more basic words; they simply tell you that something happened again. "'Recur' and especially 'recurrence' can suggest a periodic or frequent repetition, as well as the simpler notion," Merriam's notes.
If you want to emphasize that the actions keep happening, "recur" is probably the better choice. If something is happening for the second time, either word is acceptable.
Lloyd also had a good question about "that."
"Is it always better to avoid using 'that' if it doesn't change a sentence's meaning? Example: 'Mom said that I had to do my chores' vs. 'Mom said I had to do my chores.'"
No, it's not always better. Consider: "Mom knows Bob, whom she met at a conference last year, will attend the meeting."
Put a "that" in front of "Bob" and it doesn't change the meaning of the sentence. But it can help the reader get your meaning faster. Without "that," it appears that "Bob" could be the object of the verb: "Mom knows Bob." But we're not trying to say that she knows a person. We're trying to say that she knows a fact about that person: that he will attend the meeting.
If "that" offers no help to the reader, you can write it off as an unnecessary word. Just make sure that you're not creating any false impressions in the process.