I watched a YouTube video about physics, and the host said the following.

Similar to the Earth's atmosphere, the layer of haze starts out very tenuous.

If I needed to say something like this, I would have used "tenuously" (adverb) instead of "tenuous" (adjective) because that is supposed to modify the verb "start." I ran a grammar checker to see if using "tenuous" is correct there, but it didn't flag any errors. Why is using an adjective form there considered correct in this case?

  • This is more about being "idiomatically natural" than slavishly following crude rules of grammar. It's more natural to use adjectival tenuous to describe the initial state of the atmospheric layer (the part we get to first when we head up into it), rather than using adverbial tenuously to refer to "how it starts" when it's just starting to exist at its lower boundary. Nov 21, 2023 at 18:54
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    The haze is tenuous (thin and insubstantial) when it starts - it doesn't start in a tenuous way. Nov 21, 2023 at 18:58
  • @KateBunting: Of course, it doesn't actually "start" at all - it's there all the time. So we can't really think of it that way in the first place - the "start" is just the first part a sensor would encounter if it started from Earth, rather than from beyond the atmosphere. Nov 21, 2023 at 19:02
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    I'd sooner say 'the day started warm' than 'the day started warmly'. Nov 21, 2023 at 19:30

3 Answers 3

  1. An adjective can be a "subject complement". If I say "The elephant looks big," then big tells us something about the elephant, not its eyesight. In this case, "tenuous" describes the layer itself, not its "start."
  2. Note, in casual conversational usage or slang tone, adjectives are often substituted where adverbs would be formally correct. "The temperature is dropping fast."
  3. You might be a bit confused because "tenuous" was a slightly odd word choice here. It's a word that has a lot to do with behavior rather than description, and has a connotation of intent. It might have made more sense to say the layer of haze starts out "thin," "nebulous," etc. ("uh... hazy?").
  • +1 For the right answer, and to nitpick that your example of "fast" is not a good one because it's an adverb there. While to me it feels correct to say that people often use adjective forms where an adverb should be used (it's the first thing I thought of when I read the question), I can't think of a natural example where an unambiguous adjective is used to function adverbially.
    – gotube
    Nov 21, 2023 at 19:32
  • Wow thank you so much. Now I actually learned the concept of a subject complement, but it was a long ago and had even forgotten that it exists. Btw, your third point actually accurately describes why I was confused in that particular sentence lol. Nov 21, 2023 at 20:29
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    @gotube Good point; one angle might be "if it does the work of an adverb, it's an adverb!" The first example I thought of was much more colloquial, "Man, you eat messy!" Nov 21, 2023 at 21:26
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    Merriam-Webster gives as a meaning of tenuous "not dense", example "a tenuous fluid", so although this isn't the most common sense of tenuous ("shaky", "having little substance or strength") it's still a valid meaning. Note that of your suggestions, "thin" can mean "of low viscosity, flowing easily" which is distinct from density, and "nebulous" can mean cloudy/opaque, which is the opposite from the intended sense.
    – Stuart F
    Nov 22, 2023 at 13:05

The sentence is parallel to

  • This morning I awoke hungry,
  • A week after the accident, his memory returned intact,
  • Having spent the day digging ditches, she arrived home exhausted,

and even

  • The soup tasted salty.

The first example describes my state upon waking rather than my manner of waking, thus hungry rather than hungrily. One can wake suddenly, but it’s not idiomatic to speak of *waking hungrily.

Likewise, one’s memory can return fitfully (that would be a quality of its returning), but it’s not idiomatic to speak of *returning intactly. And one can arrive unexpectedly, but it’s not idiomatic to speak of *arriving exhaustedly.

As for the fourth example, when the verb to taste is used with a consumable as its subject, it typically doesn’t license adverbs, and one certainly wouldn’t say, *”tasted saltily.” Indeed, The soup tasted … means essentially The taste of the soup was …


The most common situation where an adjective following a verb should not be changed into an adverb is when the adjective is the subject complement of a linking verb. You can tell this case because such adjectives are all complements of some form of the verb "to be" or could be preceded by the phrase "as if" or an equivalent without substantially changing the meaning. In essence, such verbs are indicating some form of identity and so are incompatible with adverbs indicating manner.

An extension of this usage occurs when certain adjectives describe the state of the subject as it performs the action of the verb, the state the subject ends up in, or the state the object is in at the start or end of the action. You can identify this case, be seeing if you can precede the adjective with "(while) being...."

The phrase "the layer of haze starts out very tenuous" is an example of this extended usage. It is a reduced version of "the layer of haze starts out (while) being very tenuous."

A native speaker might also venture to say: "the layer starts out tenuously," this presupposes the semantics of a "tenuous start," which is also possible, but less idiomatic for a non-volitional subject.

Contrasting examples that clearly distinguishes the need for this extended usage are the following two sentences:

He angrily walked in.

He walked in angry.

The first sentence can suggest that the person showed visible signs of anger as he walked. It would be the equivalent of "he walked in in an angry manner." Depending on the situation, it could also be that the person was angry at having to walk in. It would then be the equivalent of "he walked in and was angry at having to do so." In either case, there is a link between the anger and the walking.

The second sentence merely describes the mental state of the person, contrasting it with other possible mental states. It is a reduced version of "he walked in while being angry." The only link between the anger and the walking is that the state of anger existed as the walking proceeded.

A common public announcement in the US is "Don't drive drunk," which means don't drive while being drunk." It does not really describe how the driving looks. If you said: "Don't drive drunkenly," it would mean "don't drive in the manner of a drunken person" and doesn't describe whether the driver has drunk any alcohol.

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