Ah, the comma. Doesn’t every wordsmith have some tiny wrinkles, etched somewhere in the mid-brow region, because of this capricious mark?

Nearly everyone has questions about the comma. Should we use a comma with and? What about after an introductory element? Is the comma even necessary today? Or is it a quaint, old-fashioned remnant of an era when readers had time to savour sentences, to pause between ideas instead of rushing madly onward, scanning for content before tackling the next task, as we so often do now?

It’s true that modern writers use commas more sparingly than their forebears. Pick up a novel by, say, Jane Austen. Open it to any page and you’ll see them—dozens of commas, swarming through sentences like ants through spilled syrup. But things are different today. Today our commas, like our technology, like our workplaces, like our very lives, are streamlined and economical, designed for speed and efficiency, not for lingering and reflection.

Still, some commas are as necessary today as ever. Properly placed commas enable readers to follow ideas and interpret meaning. Moreover, they prevent misreading. In the sentence Lynn, Massachusetts is an excellent location for our new headquarters, the omission of the comma after Massachusetts makes us think the author is assuring Lynn that Massachusetts is a great location.

The key to understanding the modern comma is to know when it’s required and when it’s not. This is no easy task; the guidelines for this minuscule mark fill dozens of pages in some texts. Thankfully, Sheridan Baker, in his fifth edition of The Practical Stylist (1981), divides necessary commas into just four categories:

1. The introducer: after an introductory clause or phrase
2. The coordinator: between two independent clauses joined by a coordinating conjunction (FANBOYS: for, and, nor, but, or, yet, so)
3. The inserter: a pair around an inserted word or remark
4. The linker: when adding a word, phrase or clause to the main sentence

The introducer

When the introductory element is a clause, the decision is easy: use a comma. (Remember, a clause is a group of words that contains both a subject and a verb.)

• After the hospital had completed its fundraising campaign, an anonymous donor contributed an additional $300,000. (introductory adverbial clause)

With an introductory phrase, the decision is harder. (A phrase is a group of words that does not contain both a subject and a verb.) If the phrase is relatively long, use a comma.

• From the east wall to the west, the "dream cottage" advertised in the real estate brochure measured just twenty feet. (long prepositional phrase)

If the phrase is short and naturally flows into what follows, do not use a comma.

• By midnight my new boyfriend was slavering and baying at the moon. (short prepositional phrase that flows on)

If the phrase is short but does not naturally flow into what follows, use a comma to show the separation. A comma is particularly important after an introductory participial phrase—one that contains the present participle (-ing form) or the past participle (-ed or irregular form) of a verb.

• Seeing his transformation, I wanted to flee like the wind. (participial phrase)
• Paralyzed by fear, I stood transfixed while my hirsute companion lumbered forward, wild-eyed and hungry. (participial phrase)
• Despite his fangs, I still thought my date was kind of cute. (phrase does not flow naturally into what follows)
• Fearful yet curious, I debated what to do. (phrase does not flow naturally into what follows)

The introducer may also appear after an introductory word that does not flow directly into the rest of the sentence, such as a sentence adverb (an adverb that modifies the entire sentence rather than just one word in it).

• Fortunately, I still had the leftover rare steak I had taken away from our lavish dinner together, so I threw it in his path to distract him. (introductory adverb)

The coordinator

Place a comma before a coordinating conjunction that joins two independent clauses (clauses that can stand as full sentences). Remember to put the comma before the conjunction, not after.

• René wrapped the fresh fish in three layers of newspaper, but his van still smelled like trout for the next week. (two independent clauses)

If the independent clauses are short and closely related, it is preferable to omit the comma.

• He chose the restaurant and she chose the movie. (short, related independent clauses)

It’s important to check that the coordinating conjunction is really joining two independent clauses and not two phrases.

• The dog whipped his head around and caught the Frisbee between his teeth. (two phrases)

The inserter

Think of the two commas around insertions as detour signs: the first tells you where the detour begins, the second where it ends.

• Margaret Atwood’s first novel, Surfacing, contains many themes and images that run through the author’s later works. (insertion)

Sometimes it’s hard to decide if a group of words is a true insertion. An insertion interrupts, meaning you can usually remove it without changing the sentence’s main message. The grammatical term for an interrupting element is non-restrictive. A non-restrictive element must be set off with a pair of commas.

• The bingo employees, who had finished their work, went home for the day. (main message: the employees went home for the day)

A restrictive element, on the other hand, does not interrupt the message; it is integral to it. Restrictive elements are not set off with commas.

• The bingo employees who had finished their work went home for the day. (main message: only the employees who had finished their work went home)

The linker

Use a comma whenever you link extra (often non-restrictive) information to the main sentence. The added information often provides elaboration.

• My sister loves low-budget horror movies from the fifties and sixties, especially those featuring killer vegetables from outer space. (added phrase)
• The sea was like a boiling cauldron, even though the wind had abated hours earlier. (added clause)

Commas also link elements in a list or series.

• Nathan took a radio, a hair dryer, the latest Vanity Fair and a canister of pepper spray on his first wilderness camping trip. (items in a list)

Should there be a comma before and in a list? It’s a perennial question, one that authorities differ on. The bottom line—either approach is acceptable, though the modern tendency is to omit the comma unless it’s needed to prevent misreading.

• Eileen’s favourite sandwiches are tuna, watercress, ham, and cheese and bacon. (comma required before and for clarity)

A pause for reflection

Knowing when we need commas is only one navigation point; knowing when we don’t is another. Between the two lies a vast and bewildering territory where comma use is subjective, dependent on such vagaries as authorial intent, emphasis and personal taste. So understanding the principles of necessary commas likely won’t erase our wrinkles (we’re not talking Botox here). But it may relax them, somewhat.

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