'Backseat' bucks a trend to become 'back seat'

Not long ago, a cellphone was a cell phone. A teenager was a teen-ager. Goodbye was good-bye. A website was a Web site. Legroom was leg room.

Words and compounds evolve all the time. But in this corner of the language world, there’s a clear trend: Two-word nouns become one word. Hyphenated nouns do the same. And it’s not just that handful of examples I gave above.

“New compounds typically enter the language in open or hyphenated forms,” writes Amy Einsohn in the second edition of “The Copyeditor’s Handbook.” “If the term gains currency, the word space or hyphen disappears and the term becomes solid.”

It doesn’t always happen. Some two-word nouns stay that way. But when change occurs, it’s always in one direction: “open” or hyphenated terms close up to become one word. It’s a one-way street.

Or it was until now. As I learned recently from a Bluesky post by Benjamin Dreyer, author of the best-selling “Dreyer’s English,”  the word “backseat” has bucked the trend. It was a closed, one-word compound in the 11th edition of Merriam-Webster’s Collegiate Dictionary. But now that dictionary considers it two words: “back seat.”

At least, that’s the form Merriam’s considers most standard. The one-word “backseat” is still acceptable as a variant.

This opening of a formerly closed word is pretty historic. But “back seat” isn’t the only term bucking the trend. “Light bulb,” Dreyer pointed out, is another. As I can confirm in my 11th edition Merriam’s dictionary, copyright 2009, “lightbulb” was standard and “light bulb” was the variant. Now, we’re back to “light bulb.”

How do these changes happen?

Regular readers of this blog know that dictionaries simply reflect how you and I are most likely to use the language. Lexicography is reportage, not rule-making. Some people hate to hear this. They think it’s wrong when dictionaries “cave” to poplar usage. But that’s not, and never has been, how language works.

Every grammar rule and every word definition came from popular usage. When grammar books or dictionaries formalize our choices, we may consider these the “rules” of language, or not. But the English language we know and love today evolved from the English language someone else knew and loved yesterday, which itself was a variation on a past iteration, all the way back to people who said “thee” and “thou.”

But the evolution of “back seat” and “light bulb” has less to do with how you and I speak and more to do with how publishers write. That is, when you’re talking, there’s no difference between “back seat” and “backseat.” So, to know how something is written, dictionary-makers rely mainly on published writing. And here’s where things get really interesting. Published writing isn’t like speech in that it doesn’t usually blaze new trails in language. Publishers tend to follow rules, so when their designated dictionary says “backseat” is one word, they write it as one word.

Except they didn’t. Comparing the history of the two spellings in published writing, we can see that, shortly after Merriam’s determined “backseat” is one word, publishers rebelled. In the mid-2010s, just as Merriam’s 2009 edition should have ushered in a trend toward “backseat," this one-word form took a big dive in popularity. So it’s no surprise that a decade later Merriam’s was forced to change course.

If you want to align your writing with the pros’, use “back seat.” If you prefer “backseat,” that’s fine, too. And if you, like some people who replied to Dreyer’s post, are wondering about the adjective form, as in “back seat driver,” you should know that there is no adjective form. There’s only adjectival use, called “attributive” in grammar speak, of the noun form. That’s what we call it when a noun like “paint” is used as an adjective in front of another noun like “store.” And because Merriam’s lists “back seat” only as a noun, it’s also the form you’d use attributively: “back seat driver,” or if you like hyphens, “back-seat driver.”

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