We’re taught a lot about proper social behavior growing up, from not chewing with our mouths open to excusing ourselves after a productive burp. But nothing is as important as knowing to call "shotgun" when you’re about to enter a motor vehicle.

“I call shotgun” is, at least in the United States, the widely-understood declaration that the speaker has claims on “shotgun,” or the front passenger seat. For a trip with multiple passengers, calling “shotgun” affirms one’s place in the most desirable spot in the car, with more legroom and a better view than the passengers stuffed into the backseat.

If you think the slang term has its roots in the Old West, you’re half-right.

When stagecoaches were common sights in the 1880s, the driver would typically assign his adjoining seat to a weapon-toting colleague whose job it was to ward off any thieves or plunderers encountered along the way. These passengers often carried shotguns, since a roaring blast from one would make it easier to hit one or more assailants from a jostling carriage. It’s natural to assume the seat grew to be known as “shotgun” for this reason alone.

And it did—just not in the Old West. No contemporaneous records exist of anyone using the term “shotgun” to describe the side seat in a stagecoach. It wasn’t until mass media became preoccupied with Western tales that the phrase began to work its way into the American vernacular, with pulp and television writers using the term “riding shotgun” to describe the presence of an able-bodied, buckshot-spitting comrade.

One of the earliest mentions came in a 1921 short story, "The Fighting Fool," by Dane Coolidge, where a character is said to be “ridin’ shotgun for Wells Fargo.” The phrase was also used in the 1939 John Wayne film Stagecoach, featuring the open decree “I’m gonna ride shotgun.”

It’s likely that these modern references to historical events led to the phrase becoming commonplace beginning in the middle of the 20th century, particularly as the new medium of television began to grow overstuffed with primetime Westerns. (In 1954, André De Toth made a feature with Randolph Scott called Riding Shotgun.)

Although rules vary from region to region, it’s commonly accepted that calling shotgun only counts when it's called outside, and in view, of a car. And if there’s a mom present, all other calls are null and void—moms always ride shotgun.

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