Simple question: Why were the prepositions "on" and "off" used for things like "The lights are on" and "The computer is off", and when did these words gain their new usage?

I'm guessing back in the days when lights were only generated by a flame people would say "The light is lit" or "The light is out", so presumably the usage began with electric lights.

Also, I've said both "The microwave is running" and "The microwave is on", but only "The refrigerator is running" and not "The refrigerator is on". Is this because of the predominance of electrical energy in the former and mechanical energy in the latter?

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    Electricity was first commonly used for lighting. I suspect that "the light is on" and "the light is off" were idioms that very quickly developed.
    – Hot Licks
    Feb 13 '16 at 13:06
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    As to your refrigerator, it's probably "on" all the time. (The light turns on when you open the door, doesn't it?) But it's only "running" when the thermostat "calls" for cooling -- that's when you hear the noise.
    – Hot Licks
    Feb 13 '16 at 13:08
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    I don't know the etymology but there's a similarity here to the flow of water from a tap, as in "turn the tap on" and "turn the tap off". I've known people whose first language was a Slavic one who would say "open the light" and "close the light". It looks to me like there's some connection to the concept of the flow of electricity. (p.s. I don't think this is a simple question8-)
    – Al Maki
    Feb 13 '16 at 17:36
  • I like the question. And I think it is a cop-out to punt to turn on/off. You can still ask the question why on/off in turn on/off - it's the same question. (And you can also ask why turn?)
    – Drew
    Feb 13 '16 at 17:37
  • @AlMaki: I think you've got it, for turn, at least. But why turn on/off?
    – Drew
    Feb 13 '16 at 17:38

Ngram finds "turn on the water" and "turn off the water" going back to 1735 at least. So clearly "turn on" and "turn off" were well-established idioms long before electricity came into common use, and they were simply adapted their electrical use as relatively mundane metaphors.

Two different (but related) guesses as to the origin:

  1. "Turn on" and "turn off" refer to diverting a stream with a small dam or gate.
  2. "Turn on" and "turn off" refer to using a petcock as might be used to control the flow of water from a cask

"Turn off" was much more common early on than "turn on", if that gives any hints as to the origin. (Perhaps "open" was used instead of "turn on"?)

Update: Looking some more, Ngram shows that "open the valve" was fairly popular since the 1700s, while "close the valve" did not perk up until about 1880, around the same time that "turn on" became as popular as "turn off". One suspects that the terminology was trying to settle, but kept being disrupted by technology.


I would have preferred to leave this as a comment because it's merely a conjecture, but I can't write a comment this long.

I think off and on may have to do with the intermittence of the light. Sometimes it's "on", sometimes it's "off". This use of off and on is documented in the OED back to the 16th century. It's even in Shakespeare's Tempest "I swam 'ere I could recover the shore, five and thirty leagues off and on." The earliest uses of it are nautical, things like "Shyppes lying off and on at Sea while under Sayle."

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    Except that it's quite unclear what "off and on" means in those quotes. One might infer a meaning closer to the modern idiom "give or take".
    – Hot Licks
    Feb 14 '16 at 19:38

"On and off" are English prepositions but they are also used as adjective/adverb/noun. It appears that before the currency of the phrasal verb 'swith on/– off' and the emergence of electrical devices, 'off and on' used to serve the same purposes as they serve now– I TAKE OFF DAY FROM MY ON-GOING PROJECT TO WRITE THIS ONLINE ANSWER BUT CAN'T SUBMIT AS I'M OFFLINE.

As we advance in scientific innovations some words gain into prominance but that doesn't rob these particles of their intrinsic meanings. In Othello's time it is 'put out the light', in mine 'swith off the light'and when the supply is off just reverse switches, no on-off.

As to "running", it is used from a commoner's perspective, he is not that particular about scientific workings so far as use of words are concerned.


"Turning off" had previously been used as a euphemism for hanging One from the neck until dead--as the condemned was often "turned" off of an object or structure, extinguishing their light. As the expression "turn off the light" predates the the use of turning on the lights, it may be that "turn on the lights" was simply the adoption of an expression that referred to the opposite of "turning off the lights" that replaced light the lights.

  • Hi John, can you provide a citation or source for "turn off" as euphemism for hanging? The typical gallows is depicted as a raised platform with a trapdoor, and a lynching using a nearby tree supposedly used a horse as both platform and platform-removal.
    – Hellion
    Aug 28 '19 at 12:43

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