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What part-of-speech is "running" in the following example?

  • The car comes with daytime running lights.

Is it a noun, verb (gerung), adjective, or something else?

  • It functions as an adjective (as does "daytime"). Different "schools" of syntactic nomenclature will give it different names. – Hot Licks Aug 27 '18 at 20:57
  • Yes. I agree with @HotLicks. And I would definitely hyphenate 'daylight-running'. – WS2 Aug 27 '18 at 23:09
  • @HotLicks It's not an adjective: the lights are not running. They're for running. It's a noun-noun compound. Make that a noun-noun-noun compound for daytime running lights: just three nouns together and no adjective in sight. – tchrist Aug 27 '18 at 23:48
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    @tchrist - Like I said, it functions as an adjective. Its use in sentence construction is essentially identical to a "real" adjective. And I've given up trying to remember what the "official" name is, as that changes every 10-20 years. – Hot Licks Aug 27 '18 at 23:56
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    @tchrist - "Daytime" modifies the noun "running lights". It's NOT "daytime-running". The entities we're talking about are "running lights". "Daytime" tells you that they are activated in the daytime. In "thin red post" "thin" does not modify "red". – Hot Licks Aug 28 '18 at 0:05
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https://en.wikipedia.org/wiki/Daytime_running_lamp

Technically, it's a lamp (=lights) indicating a state, and that lamp is for usage at daytime.

'Daytime' acts as an adjective here, like 'night' does in the combination 'night bomber' where night can't be an object, since it's not about 'bombing the night', it's about night usage. That adjective applies to the combination 'running lights' where lights is definitely a noun. Unlike 'daytime' the gerund 'running' there functions like a noun, since the lights don't run and just indicate the car engine's state name called 'running'. That name could be any noun phrase. So the word in question is a gerund in function of a noun.

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A running light is an open-form noun, as per its entry in Merriam-Webster:

: any of the lights carried by a vehicle (such as a ship or automobile) that indicate size, position, or course

Running simply forms one of the components of the noun.

It's the same type of open-form noun as ice cream.

The only adjective in the phrase is daylight.


Despite the fact that its origin most likely comes from lights that indicate something is "turned on" (running), and running would have at first have been used adjectivally, the components are now simply functioning as parts of a whole.

This is, again, similar to ice cream, which was initially known as iced cream until the adjectival iced became part of the single word—and the d was dropped due to common pronunciation. Or like laser, which originally stood for light amplification by stimulated emission of radiation but is now "just" recognized as a word in its own right.


In response to a comment, since it's a common noun (no pun intended), there is no need to use hyphenation—just as there is no need to hyphenate chocolate ice cream. The correlation between all three words is not something that would be commonly misunderstood.

  • They're lights for running, so just a noun-noun compound. It was never an adjective, no more than it was in running shoes. People get this wrong all the time. Attributive nouns aren't adjectives. Easily confused with the situation of running water or running gazelles, which are indeed adjectival uses. But not running shoes or running lights. – tchrist Aug 27 '18 at 23:49
  • @tchrist I both do and don't agree with this analysis. A light may be flashing, but it's not used for flashing. Similarly an engine may be running, but it's not used for running. If something is turned on, it can be considered to be in operation—or running. In this sense, a running light is a light that is shining or active. Running is used to describe its current state. In that sense a household light that's been turned on could also be called a running light. However, a running light on a boat can be either on or off, so I agree that it's not actually adjectival in this use. – Jason Bassford Aug 28 '18 at 0:09
  • @tchrist (Assuming that we're talking about the compound noun as opposed to the simple noun, which I was in my answer.) – Jason Bassford Aug 28 '18 at 0:13
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    Well, you're saying that daylight is an adjective. How can that possibly be? If you had daylight sensors, those sensors wouldn't be daylight, so that fails the predicate test for adjectives. And they could never be very daylight sensors either, so that fails the very test for adjectives and adverbs. And they can't be more daylight sensors than these other ones here, so that fails the comparative degree test for adjectives and adverbs. What syntactic test can you present supporting your hypothesis? Surely daylight can only be a noun here. Attributive nouns aren't adjectives. – tchrist Aug 28 '18 at 1:26
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    @rustyx Yes, that's correct. No matter how it's looked at, running is being used as a noun in this context. – Jason Bassford Aug 28 '18 at 14:55
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Wikipedia:

A navigation light, also known as a running or position light, is a source of illumination on a vessel, aircraft or spacecraft. Navigation lights give information on a craft's position, heading, and status. Their placement is mandated by international conventions or civil authorities. Navigation lights are not intended to provide illumination for the craft making the passage, only for other craft to be aware of it.

On boats and aircraft these "running lights" are normally only lit at night, so similar lights adapted to daytime use on automobiles are qualified with "daytime".

The lights were called "running lights" because they were only required when the vessel (generally a steamboat) was "running", ie, underway. The basic scheme and much of the nomenclature was adapted to aircraft when they became common enough to create a collision risk.

The automotive sense was no doubt "borrowed" from the nautical sense. But the "daytime" qualifier was added, not because the lights were extinguished at night, but because they were lit during the day, in contrast to nautical lights.

(Yes, this "answer" doesn't directly answer the original question, but I hope it clears up some of the confusion around the terminology. Downvoting it won't hurt me, but it will make this info unavailable to low-rep users here.)

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