Many people think that whether to put a comma before “and” in a series is a trivial issue, but two judges disagreed.

For decades, people have bickered about the need for a comma before “and” in a series of three or more things. Some people insist on it, and others sneer that it’s not necessary, but a court case in Maine shows that the comma can affect the meaning of a sentence.

Truck drivers sued a dairy company for more than four years’ worth of overtime pay, worth about $10 million. The company argued it did not owe the drivers money because they were exempt under the law. The  U.S. Court of Appeals in Boston said the absence of the comma in a series (called the serial or Oxford comma) made the law unclear, so it ruled in favor the drivers.

Here is where the comma before “and” can make a difference. In We have several types of vehicles, including motorcycles, cars and trucks, some people will insert a comma after cars; others won’t. Whether it’s necessary, depends whether cars and trucks represents one category of vehicles.

Lawyers for the Maine dairy said state law does not require companies to pay overtime to drivers who are engaged in canning, processing, marketing, storing, packing for shipment or distribution of perishable foods.

The court said that without a comma, it was unclear whether the law referred to packing for shipment as one activity and distribution as another, or whether the law referred to drivers who perform one task called packing for shipment or distribution.

It was a key issue, because the dairy’s delivery drivers don’t pack perishable foods, but they do distribute them. A comma after shipment would have made it clear that the law applies to people who ship and to people who distribute. The absence of a comma created enough uncertainty, the court said, that it could not rule in favor of the company.

This is not the first time punctuation has figured into a major court case. In 2004, when many gay and lesbian couples were marrying in San Francisco, conservatives filed a court order urging the judge to cease marriage of same-sex couples, and a judge said the use of a semicolon rather than a comma changed the meaning of a sentence. He refused to grant the request.

Takeaway tip: To avoid the risk that the reader will misread the sentence, insert the comma.

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Ken O’Quinn teaches communication workshops in corporations. A former Associated Press writer, he teaches business writing, managerial communication, and journalistic writing for communicators. He is a contributing author of a new book on leadership titled “Focus on Them.”