Linda M. asked the following question in a Facebook message:

My mom used to say, “Never use a comma before any form of the verb to be.” Is this right? In some sentences it seems like there should be a comma before the word is.

I find this rule curious and wonder how such rules get created and passed on. It’s not wrong either, at least not entirely. Let’s see if we can clarify it a bit.

First, the general rule is not to use a comma to separate a verb from its subject. The concern isn’t that the comma come before the verb but that it come between the subject and its verb. In general, don’t do that.

Second, there’s no need to limit the rule to be-verbs. It’s just as wrong to place a comma between a subject and an action verb as it is to place it between a subject and is, are, was, or were.

Third, the rule has some exceptions (Ain’t that always the way?). If the sentence includes a parenthetical phrase or nonessential clause between the subject and its verb, you’ll need to set off that phrase or clause with commas.

For example:

Frank, flummoxed the family of flamingos. X  Wrong. No need for this comma between subject (Frank) and verb (flummoxed).

Frank, in case you were wondering, flummoxed the family of flamingos. √ Correct. In case you were wondering is a simple parenthetical expression — an interruption that is syntactically unnecessary to the sentence — and needs to be set off with commas even though it happens to come between the subject and the verb.

Frank, my favorite firefighter, flummoxed the family of flamingos. √ Correct again. This parenthetical construction is known as an appositive phrase and likewise needs to be set off with commas.

Frank, who fears feathered creatures, flummoxed the family of flamingos. √ Also correct. Here you have a nonessential clause, which needs commas.

Here’s my revision of Linda’s mom’s rule: Don’t use a comma to separate subject and verb. If a nonessential clause or parenthetical phrase comes between them, fine, you need commas to set it off as usual, but the purpose of the commas is not to separate subject from verb.

For more comma rules go here. Or here.

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