A supermarket recently opened in my neighborhood. The managers promptly posted a sign boasting “Low prices everyday.”

This is a frequent error, though that doesn’t make it any less excusable. The sign should read “Low prices every day.”

The adjective everyday precedes a noun, as in “The life of the medieval peasant was filled with everyday chores.” But every day means “each day,” as in “I commute to work every day.” In this example, the phrase is an adverb that modifies commute.

A rule of thumb is that if you can substitute “each day,” the two words every day are correct. If not, the single word everyday is most likely the right choice.

It can be tempting to conclude that a pair of words can be turned into a compound word without affecting the meaning. But this assumption isn’t always true. Other common mistakes of this sort include alright (which should be all right) and alot (a lot). Unlike everyday, though, neither of these erroneous compounds is a legitimate word.

The lesson: Be careful with lookalikes, or what the French vividly call “false friends.”

[Ed Note: For more than three decades, Don Hauptman was an award-winning independent direct-response copywriter and creative consultant. He is author of The Versatile Freelancer, an e-book that shows writers and other creative professionals how to diversify their careers into speaking, consulting, training, and critiquing.]

Don Hauptman was an award-winning independent direct-response copywriter and creative consultant for more than 30 years. He may be best known for his headline “Speak Spanish [French, German, etc.] Like a Diplomat!” This familiar series of ads sold spectacular numbers of recorded foreign language lessons for Audio-Forum, generating revenues that total in the tens of millions of dollars. In the process, the ad achieved the status of an industry classic. Don’s work is mentioned in three major college advertising textbooks, and examples of his promotions are cited in the books Million Dollar Mailings (1992) and World's Greatest Direct Mail Sales Letters (1996). In a column in Advertising Age, his name was included in a short list of direct-marketing “superstars.” He has a parallel career as a writer on language and wordplay. His celebration of spoonerisms, Cruel and Unusual Puns (Dell, 1991), received rave reviews and quickly went into a second printing. His second book was Acronymania (Dell, 1993). Recently, Don retired from full-time copywriting in order to focus on other interests, including his passion for “recreational linguistics.” He is at work on a new book in that genre. He is a regular contributor to the magazine Word Ways and writes “The Language Perfectionist,” a weekly column on grammar and usage, for Early to Rise. Don is author of The Versatile Freelancer,an e-book from American Writers and Artists, Inc. (AWAI) that shows copywriters – and almost anyone – how to diversify their careers into consulting, training, critiquing, and speaking.