How do commas separate the essential from the nonessential in a sentence?
Editing punctuation for clarity
[An earlier version of this article was published early in 2024. For the foreseeable future, I’ll publish a revised or brand-new editorial help article semi-weekly.]
The Short Story
One of the main ways we use punctuation is to separate groups of words. Commas, and sometimes other kinds of punctuation, can set apart nonessential words—those that leave intact the main thought you’re getting across.
The Real(ist) Story
A word (or group of words) that makes a critical difference to the meaning of another word (or group of words) in the same sentence is essential. If the first word (or group of words) is only a helpful or interesting elaboration—an add-on, so to speak—it’s nonessential.
If a sentence were a house, the essential clauses and phrases would be the structures and features built into the house itself: the frame, the roof, the walls (load-bearing and otherwise), the flooring, the plumbing and electric, the HVAC, and so forth. Some of these elements may be more decorative than functional, but removing or changing them would alter the house itself. You’d have to edit the real estate listing if the house were on the market.
The other, nonessential stuff isn’t unimportant. If it were, you’d probably leave it out completely. But it’s fundamentally decorative. It elaborates on the essential stuff in ways that may transform the personality of the sentence, yet the gist remains intact. A change in paint, decór, furniture, or landscaping may affect the appeal and value of a house, but it constitutes redecorating, not remodeling.
In writing, the words themselves aren’t always enough to tell your readers which words are essential and which are nonessential. Commas are the default, least obtrusive way of fencing off nonessential bits, like the picket fences of punctuation, though occasionally a chain-link fence (parentheses) or barbed wire (em dash) may be called for.
If you use commas, parentheses, or em dashes to separate groups of words unnecessarily (for instance, if those words are essential to the meaning of the sentence), you might interrupt the flow of the sentence (how rude!) or create room for confusion.
On the other hand, if you don’t use commas (or other appropriate punctuation) to distinguish the nonessential stuff from the essential, you’re playing with editorial fire. Your sentence may technically mean something very different from what you intend. Maybe the misreading is so ridiculous that it won’t trip up most readers. But why take the chance?
Story Time
The sea-folk warrior who had drawn the short straw was expected to carry the banner into battle.
In the sentence above, the clause who had drawn the short straw is essential because there’s no punctuation to set it apart. The implication is that there are many sea-folk warriors, so it’s essential to specify the one who drew the short straw.
The sea-folk warrior, who had drawn the short straw, was expected to carry the banner into battle.
In the sentence above, the clause who had drawn the short straw is nonessential because of the commas setting it apart. The implication is that of all the sea-folk in existence, only one is a potential candidate for the subject of this sentence. The fact that he or she drew the short straw is simply extra info or a helpful reminder to the reader.
Godspeed and happy rewriting!