The sky is dark blue.


BBC English

Catherine: The sky is dark blue. The sky is dark blue.

Finn: So, is blue an adjective or adverb?

Catherine: It’s an adjective. Blue is describing the noun sky. Now number two: it's actually the same sentence but this time, think about the word dark. Is dark an adjective or an adverb?

Finn: The sky is dark blue.

Catherine: Right. So, is dark an adjective or adverb?

Finn: Dark here is an adverb.

Thanks for the discussion.

It is interesting to read how the discussion is geared towards the possible explanations of the usage of dark as an adverb.

I've checked several dictionaries before starting this post. Dark is NOT an adverb. If dark is not an adverb, how and why can it be used as an adverb?

In this case, what is wrong to have dark as an adjective in the sentence?

  • 2
    The linked video doesn't work for me, so here's a link to the lesson transcript. In there Catherine says You mentioned that referring to verbs was only one thing that adverbs do. So, where else can we use them?, to which Finn replies Adverbs can also describe adjectives, and even other adverbs. So essentially this is a matter of terminology - there's no adverb in The sky is dark or The sky is blue, but there is one in The sky is dark blue. Jul 14 '19 at 15:29
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    The function of dark in dark blue is as a secondary modifier (in this case, an adjective modifier). Some think that that's so different a role from verb modifier that it should be classed differently from adverbs in a separate category, but most class it as an adverb in this usage. Jul 14 '19 at 15:48
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    @FumbleFingers That source is wrong. Hues can only ever be darker blue, never dark bluer. :)
    – tchrist
    Jul 14 '19 at 21:16
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    @EdwinAshworth I can find no reputable source that classifies dark in dark blue as an adverb. Ditto for light, pale, faint in such compounds as light grey, pale lavender.
    – tchrist
    Jul 14 '19 at 21:20
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    I have checked several dictionaries before posting this. Dark is not an adverb.
    – Jalene
    Jul 15 '19 at 2:38

The answer to the question “Why is dark an adverb in this sentence?” is that it is not one; that source is wrong. That’s because dark cannot ever be an adverb, let alone here. It’s just that color-words can behave somewhat curiously.

We have various related questions about this curiosity, including this one. John Lawler’s suspicion about color words having a special dispensation seems instructive:

John Lawler: Blue is the name of a color; names are usually nouns. I suspect we have a special dispensation for color words, like we do for many other semantically-crucial word sets.

Greg Lee: @JohnLawler, of course "blue" is a noun. I would never deny that, nor does McCawley. That's why, he reasons, it can be modified by the adjective "dark".

So it seems colors can be nouns for modification purposes in that they take adjectives to qualify them. The resulting multiword compound, the adjectivally qualified color like dark red or robin’s egg blue, is used to further describe another noun. The whole compound can then be qualified by intensifiers like very.

I'm guessing that we can use adjective ordering rules and perhaps constituency tests to show that the whole multiword part about the color counts as one single syntactic constituent. Therefore you must look at grammatical roles these phrases play in the grammar, not at the internal parts of speech of individual words within that phrase. Otherwise you get nonsense results the way you get when a gerund clause’s head VERB-ing word gets mistakenly called a noun when it’s really a verb. Calling it a noun is a common error — but calling is only a verb there at the start of this sentence, not a noun. I suspect this is the same class of error in calling dark an adverb when it’s actually an adjective.

What the Dictionary says...

Regarding blue, the OED says:

Often with modifying word indicating intensity (as bright blue, dark blue, light blue, etc.), drawing a comparison with an object or another colour (as indigo blue, lavender blue, powder blue, etc.), or making a (sometimes arbitrary) association with a person or thing (as French blue, royal blue, navy blue), etc.

But those “qualifying words” certainly are not adverbs. Indeed, the OED says that dark is an adjective when it has this color-related sense:

3c. Prefixed, as a qualification, to adjectives of colour: Deep in shade, absorbing more light than it reflects; the opposite of light. (Usually hyphened with the adj. when the latter is used attributively.)

And here are two citations provided of this:

  • 1859 J. Ruskin Two Paths v. 202
    That lovely dark purple colour of our Welsh and Highland hills is owing, not to their distance merely, but to their rocks.
  • 1863 M. L. Whately Ragged Life Egypt xvii. 163
    Clad in the ordinary dark-blue drapery.

Rubber Baby Buggy Bumpers

Why do they say this is an adjective? If you think it through, you’ll see why dark cannot be an adverb here, only an adjective.

What’s your favorite color?
Hot pink.
You mean like your hot pink sunglasses?
Exactly! All my sunglasses are hot pink!

If someone tells you their favorite color is hot pink, it seems reasonable to call pink a noun and hot an adjective. But now applying that to sunglasses doesn't swap around all the parts of speech into something new.

This happens with colors all the time:

  • cerulean blue skies
  • cherry red sunsets
  • cobalt blue skies
  • safety green vests
  • royal purple stoles
  • saffron yellow robes
  • robin's egg blue eyes
  • electric pink sunglasses

The last word in each of those noun phrases is a noun, but the first word of each is not an adverb. It is either a noun or an adjective in each case. Cobalt is a noun; it does not suddenly become an adjective when talking about a cobalt blue nor does it become an adverb when it is used in our cobalt blue skies

This is just like how tinted is not an adverb in tinted glass windows, or like how in the whole tongue-teaser rubber baby buggy bumpers, there are no adverbs nor even any adjectives.

  • 4
    While "dark bluer" is ungrammatical, "more dark blue" is grammatical, at least for me. (And the meaning is different from "darker blue"--the "more" is modifying the entire compound adjective "dark blue".) Jul 15 '19 at 2:24
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    @tchrist Right. Before starting this post, I have checked several dictionaries and dark is never an adverb.
    – Jalene
    Jul 15 '19 at 2:25
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    Simply because you can't grade "blue" doesn't mean it isn't an adjective. There are plenty of adjectives that are not gradable in general (e.g. *boringer), and it is not that curious that preceding a normally gradable adjective with an adverb might make it ungradable. Your position that "blue" is not an adjective becomes less defensible when, rather than it being a subject complement of a copula, it is directly modifying a noun, e.g. "Look at the dark blue sky". Jul 15 '19 at 18:20
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    @tchrist I don't know what point you're trying to make here with the comment about "red" and "rose". The theory that anything that modifies an adjective (or verb) is an adverb is commonly taught by grammarians. I disagree with that theory (if for no reason other than possessives, such as "Bob's sister's dog's dish", which clearly modify nouns, but are modified as if they are nouns) but the "if it modifies an adjective, it's an adverb" rule is commonly taught nevertheless. Jul 15 '19 at 19:32
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    @Jalene The most well-suited place is a grammar (the most expansive and popular is the Cambridge Grammar of the English Language (CGEL) by Pullum & Huddleston, but it’s very big and very expensive), but it can often be hard to find a section that deals with a specific use of a specific word in grammars. Sadly, there are no good reference works which list word classes, in part because word classification is a complex and unfixed matter. It would be nice if dictionaries were more reliable in this aspect, but their classifications are based on outdated models, too numerous to update now. Jul 16 '19 at 19:51

Adjectives are used to describe nouns, i.e. the car is red.

Adverbs are most commonly used to describe verbs, i.e he fought valiantly

But adverbs can also describe adjectives. How is the car red? Is it blazingly red? Is it cheesily red? Cheekily red maybe?

That is the case for your sentence. The sky is blue. How is it blue? Darkly. It is not being blue lightly, it is being blue darkly.


It doesn't always need to be this way. One can also have adjective combinations, which would be what most would assume the sentence in question is employing. An adjective combination is where two conceptually separate adjectives join to describe one concept. Dark blue is an adjective, built by two, working in a combination. The sentence in question is ambigious in that sense, as we can't know whether it's an adverb describing an adjective, or an adjective combination. The only person that can really decide that, is the author. But in this case, it doesn't really matter which one it is, as the meaning remains the same either way.

  • 7
    IOW, "darkly" describes "is", not "blue". Think teen angst.
    – RonJohn
    Jul 15 '19 at 2:08
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    Yeah, I've never thought of that. Adverbs that "are describing adjectives" are really just describing the verb "to be". @RonJohn
    – A. Kvåle
    Jul 15 '19 at 16:15
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    The word in question is not "darkly", it's "dark". So I don't see how the discussion about "darkly" is relevant.. Not to mention that I don't think "darkly" really ever has that meaning. You would never describe a dark blue sky as "darkly blue".
    – Blorgbeard
    Jul 15 '19 at 18:15
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    @Blorgbeard Yes, I was agreeing with you. I chopped up the comment a little oddly upon edit and left it less than stellarly clear.
    – tchrist
    Jul 15 '19 at 20:27
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    @Blogbeard My read of it is that omitting the ly and using dark to mean darkly might be a sort of old-fashioned and/or poetic affectation. Changing the word order might help: "Dark the sky is blue."? The original quote, I think, is claiming that this change is not even necessary for it to have the alternate sense. Can't come up with a good similar example offhand, but I'm imagining something Tolkeinian.
    – dgould
    Jul 16 '19 at 0:32

It's used as part of a set phrase which acts as an adjective. That being said, it's easy to imagine an adverb answering the question "how", as in

Q: "How blue is the sky?"
A: "It's dark blue." <- possibly an adverb, with the meaning that it's mostly black and a little bit blue


A: "It's slightly blue" <- definitely an adverb

  • @IlmariKaronen yes, that's what I meant. I'll edit my answer. Jul 16 '19 at 14:27

It might be an adverb, or it might not be, depending on which "authority" you want to listen to. The English language has been around for much longer than our attempts to systematize it and slap labels on things, and our fumbling attempts to do so are crude at best. There's clearly no dispute here about meaning or usage, and it diagrams nicely either way, so I see no particular reason to be pedantic about it.

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