When a society gets out of hand, a government can try to “marshal” its forces to settle things. But the news article said that “streams of pedestrians and heavy commuter traffic have replaced Mexican soldiers and armored military vehicles that helped enforce marshal law 18 months ago.”

That may sound right, but it’s not. The word wanted there is “martial.”

The “marshal” is the lawman the townspeople called in when things got out of hand in the Old West. The original “marshal” was a groom or farrier, someone charged with taking care of horses. Later, the “martial” took charge of other household affairs, and eventually military affairs. “This development reflected the importance of the horse in the medieval state,” The Oxford English Dictionary says, “especially the importance of cavalry in medieval warfare … and had already taken place before the word was borrowed into English.” A “marshal” is also someone who performs organizing duties, ceremonial and otherwise, as in a “parade marshal.” Today, most municipalities still have “marshals,” but most carry subpoenas or eviction notices instead of six-shooters.

Since most of those definitions have to do with the military or law enforcement, it seems logical that a government decree putting the military in charge would be spelled that way. Not helping is the comic book Marshal Law (a satire on other superheroes) and a couple of TV series with “Marshal Law” in their titles. But while “marshal” has at its root Anglo-Norman/Old French word marescal, or “horse servant,” “martial” has at its root the god of war, Mars. A government imposing military rule is in effect declaring war on its own people; thus “martial law.” Taekwondo, kung fu, karate, and other techniques that have their bases in self-defense or fighting are “martial arts.”

As a verb, “marshal” means “to arrange in order”; whether its past and participial forms are spelled “marshalled/marshalling” or “marshaled/marshaling” is largely a matter of style, though Americans tend to leave out the second “l.” But only proper names are allowed to have that second “l” in the basic form, noun or verb.

The confusion of “marshal” and “martial” is nothing new; the OED says that “variant spellings” of them “make it clear that the two had become homophones by the end of the 16th cent.” But it seems to have increased in recent years, possibly aided by spelling checkers that can’t tell them apart. Enough people confuse them that Garner’s Modern American Usage lists “marshal law” and “marshall” at Stage 1 of its five-stage Language-Change Index, meaning only people who rely on comic books or TV for their spelling lessons think they’re OK. That proves once again the wisdom of Marshall McLuhan’s words about medium and message.

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Merrill Perlman managed copy desks across the newsroom at The New York Times, where she worked for 25 years. Follow her on Twitter at @meperl.