Three women “on” a car. Photo credit: anyjazz65, Flickr.
Answer: The most accurate answer, according to Ken Litkowski, a computational lexicographer specializing in prepositions, is “just because,” which is why non-English speakers have so much trouble with prepositions. The Oxford English Dictionary defines “on” as “traveling in a public vehicle, meaning you should be “on” a car just like you’re “on” a bus or train, even though you’re “in” all of them.
This seeming dissonance has deep roots. Historically, according to Ben Zimmer, executive editor of Vocabulary.com and language columnist for the Wall Street Journal, “on” was used for pre-carriage conveyance, as in “on a horse” or other animal. Then came vehicles that were basically open platforms, which you would also sit “on.”
“Once this use of ‘on’ was established,” Zimmer says, “it came to be used for riding any large vehicle even if it’s enclosed, like ‘bus,’ ‘train,’ or 'plane.’ You can blame the inertia of English speakers that this usage of ‘on’ lingered for those big vehicles, even while ‘in’ came to be used for ‘carriage,’ 'coach,’ and eventually 'car.'”
Photo credit: Chris Gladis, Flickr.
Prepositions are mercurial in nature, says Gina Cooke, a linguist from Eureka, Ill. She says they “vary from language to language, and sometimes from region to region. You could find at least 100 examples in English of this kind of inconsistency. The reason, ultimately, is because language doesn’t have to follow logical rules. The question, she says, contains an underlying false assumption that all nouns that share a given quality or function will take the same preposition in a phrase, but it’s just not so. In this specific case, “bus,” “train,” and “plane” carry multiple passengers, but “car,” “truck,” “van,” etc., can carry just one or a few.
Zimmer says that he’s seen the distinction explained to English language learners that you use “on” for public/commercial transportation and “in” for private/personal transportation. That’s a decent rule of thumb, but it doesn’t always work. Do you need to know whether a boat is private or public whether you ride on or in it? Are you really going to say that you’re “in” an Uber? Can you simultaneously be “in” and “on” the subway?
This mystery will probably never be fully solved. But if an answer does emerge, we’ll be on it immediately, or maybe in it. Depends on what kind of vehicle we’re on or in at the time.
We’re scouring the Internet to uncover interesting questions that people have posted looking for advice from the unwashed masses. We will contact experts to give you well-researched, professional advice. You can also submit questions to firstname.lastname@example.org.