Neal Pollack, “Question Of The Day: Grammar Help Needed, Please!” (Yahoo Autos, July 22, 2015)
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.’”
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