Indefinite articles used with plural nouns: It was AN amazing TWO DAYS

Question

The indefinite article a(n), derives from the old English word an meaning "one". Generally this word only occurs in determiner function before noun phrases which are singular. However, there seem to be some cases where this determiner occurs before plural noun phrases. I say that, but actually these noun phrase seem so bizarre to me, in terms of their structure, that I'm not sure they're definitely noun phrases at all. Here are some examples:

• a full three months before we left
• an amazing two days
• an awkward ten minutes

Ignoring the article here for a moment, these noun phrases are odd because the adjective is occurring before the numeral. We would normally expect to see:

• three full months
• two amazing days
• ten awkward minutes

Even given the oddness of the word order in the original phrases, I can see no reason why the normally singular indefinite article is licensed here.

Can anybody give an account of the syntactic structure of these phrases, and/or explain why the semantically singular article is able to be used with such phrases - even if they compulsorily trigger plural verb agreement?

Here is an example of one of these instances which seems to demand a plural verb:

1. An amazing two million people attend every year.
2. *An amazing two million people attends every year. (ungrammatical)

Answer 1

A few old grammar rules

A great many, a good many, a few.—These are very incorrect and bad phrazes; and the singular article can never be properly used with a plural noun.

Since Few words on Many Subjects was published in 1831, English has seen quite a few changes. I don't know whether this rule was enforced at schools, but I did find another example lambasting the use of the indefinite article before many in front of a plural noun.

There is an extensive and growing error in the use of the adjectives good and many. It is not correct to say “a good many apples,” tho we may say “many good apples;” for, omitting the adjective good, we can not say “a many apples.” Neither is it correct to say “a great many persons;” for, “a great persons,” or “a many persons,” would be improper. It would be better to say, many apples; many persons, and omit the good and great. We do not hear of “a bad many,” or a “small many.” Why then say “a good or great many?” “The rushing of many waters;” “the influence of many minds,” are much more expressive than to add the words great and good.

^{Source: A grammar of the English language: Explained According to the Principles of Truth and Common Sense ... (1839)}

a/an + adjective + number + plural noun

The fact that native speakers were using the article "a" in front of adjectives and plural nouns in the 19th century, proves there is nothing new under the sun. Today the following sentences are perfectly grammatical.

1. He weighed a whopping twenty-five stones (350 lbs)
2. We spent a wonderful/fantastic/memorable three weeks in Greece
3. He had collected a good many books
4. She waited a full three minutes before speaking
5. It had been an exciting two years for Alice
6. Ted had an exhausting two days in Denver.
7. It costs a mere twenty dollars.

In sentence 3, “a great number of” could substitute “a good many”.

(a) He weighed twenty-five stones.
(b) We spent three weeks in Greece.
(c) He had collected many books.
(d) She waited three minutes before speaking
(e) Alice had experienced two exciting years.
(f) Ted had two exhausting days.
(g) It (only) costs twenty dollars

The sentences are only grammatical without the "a" and its "adjective"; take away only one of the two components, and the sentences become ungrammatical. The indefinite article modifies the adjective with the number. There has to be a number attached to the adjective in order for the sentence to be grammatical.

“She waited a full minutes before speaking” (NO)
“She waited a three minutes before speaking.” (NO)
“She waited a minutes before speaking” (NO)

The noun phrases take a plural noun and a plural verb after the singular a great /good many; or a/an + adjective + number; e.g.

A great many people in this country are worried about law-and-order
An astronomical 300,000 tons of apples were destroyed.
… an amazing 250,000 new neurones are added every minute.

In a great (or) good many people, “great” and “good” act like the adverb very, or really, they intensify the adjective many; i.e. “very many people” and “really a lot of people”.

The determiner many and a good many are listed in all the dictionaries I checked, but they offer no insights as to why this construction is acceptable.

many n. (used with a pl. verb)
1. The majority of the people; the masses: "The many fail, the one succeeds" (Tennyson).
2. A large indefinite number: A good many of the workers had the flu.
^{American Heritage® Dictionary of the English Language}

man•y
3. a large or considerable number of persons or things: A good many of the beggars were blind.
^{Random House Kernerman Webster's College Dictionary, © 2010}

Rogermue in the comments, suggests that a great many is derived from the German noun Menge a word meaning "multitude".

An article in Language Log has this to say on this particular construction

Funky a

A couple of days ago, I took Roy Peter Clark to task for claiming that phrases like "a million dollars" show that the indefinite article a can be used with a plural head ("Slippery glamour", 7/4/2008). I observed that the structure is clearly [[a million] dollars], not [a [million dollars]]; that expressions like "a million" are just numbers, fitting into the normal syntactic slot where numbers go; and that million in this case is morphosyntactically singular.

In the comments, Russell Lee-Goldman pointed out that
There are, however, a few cases where it really looks like "a" is acting funky:

– He was there for a good seven years.
– An additional three people are required.
– A mere four nations recognize that standard.
– She collected an amazing and heretofore unprecedented forty million dollars.

[..examples taken from the web...]

But these examples seem to me to represent a generalization of the phenomenon on display in phrases like "a million dollars": English number-expressions have inherited from their partitive history a limited ability to act like singular noun phrases.
However, I'll admit that the constituent structure doesn't feel like

[ [a <modifier> <number>] <noun>]

but rather feels like

[ [a <modifier>] [<number> <noun>] ]

— for what little those feelings are worth

The article ends with an update and suggests reading two studies. The paper, A SINGULAR PLURAL, by Tania Ionin & Ora Matushansky, I believe would interest the OP a great deal.

Answer 2

OK. I think the singular article is used because in each of your examples the plural nouns make up a single unit of time. The same structure would be used with other units of measurement:

a weighty three bags of coal

a full ten bottles

an arduous eighty kilometres

In such case, the unit of measurement is the noun phrase which includes the amount: "three months"; "ten bottles"... so the adjective comes, naturally, before that noun phrase.

Without the article, there is no single unit, so the quantities refer to multiple units, which are therefore plural nouns and take their adjectives just before themselves.

Does that make sense?

Answer 3

If you have a structure as "an amazing two days" a noun+of has been dropped:

an amazing period of two days

In other structures of this type you have to insert an analogous noun.

Answer 4

I can't help but notice a similarity between sentences containing the construction you've isolated (indefinite + adjective + unit of measurement) and sentences containing collective or group nouns like 'committee'. They both can appear with indefinite articles in singular and plural contexts, for example:

1. It was an amazing two days. [singular]

2. They were an amazing two days. [plural]

3. It was an amazing committee. [singular]

4. They were an amazing committee. [plural]

Collective or group nouns are strange because sometimes they require verb agreement in the singular and sometimes they require it in the plural, for example:

5. The committee is going to New York. [singular]
6. The committee are eating with their families tonight. [plural]

It depends on whether the situation being described involves the committee acting as a unit or as individuals.

It seems like a similar duality exists with seemingly plural noun phrases of time and measurement (for example, 'two days'). They, like collective nouns, can be conceptualized as referring to a holistic unit or as a collection of discrete individuals. The conceptualization as a unit licenses the use of the indefinite.

To see that 'two days' exhibits a similar duality, just consider that this phrase, taken bare, can (seemingly) license both a singular and a plural verb:

7. Two days is not enough. [singular]
8. Two days are not enough. [plural]

Answer 5

Sometimes, English doesn't seem to work logically. An indefinite article is supposed to be placed before a singular noun or noun phrase.

A month is a long period.

*A two months is a long period. (Ungrammatical)

But depending on how you perceive two months, you can treat two months as a singular unit (quantity of time) as in:

Two months is a long period.

?Two months are a long period. (Not idiomatic)

Related question: Is it “5–6 weeks are a lot of time” or “5–6 weeks is a lot of time”?

But if you contrast

1. Two months have passed since he died.

2. Two months has passed since he died.

nobody could confidently argue that No. 2 should always be used. There is no reason not to use No.1 if you think of each day of the two months as a unit of period passing for sixty days (two months).

---

Now, using "a/an" before plural noun phrases seems to be inconsistent.

1. It has been an amazing two months - It is grammatical as "two months" could be replaced by "an amazing period of time" which is singular. However,

2. *It has been a two months. - It is ungrammatical because the indefinite article is not supposed to be placed before a plural noun. It is inconsistent. You can replace "two months" with "a period of time" here, too.

Does it mean the indefinite article is allowed in No. 1 just because there is an adjective amazing? It doesn't make any grammatical sense. An article is not supposed to modify an adjective except for a few exceptions, e.g., the old, the young, etc.

The only logical and grammatical answer seems to be what @Rogermue suggested, i.e. [period (or its equivalent) of] is omitted (or a plural noun is perceived as a single unit as a quantity of time). For example:

1. [A period of] two months is a long time.

2. It has been an amazing [period of] two months.

Then, why does only No. 1 allow the indefinite article to be omitted whereas No. 2 doesn't?

Because it is separated from the noun.

There is a similar grammatical pattern in placing the definite article before a comparative. The following is what Bernie Sanders said on ABC This Week yesterday.

... I ask those super delegates to take a look at which candidate is the stronger candidate to defeat Donald Trump. Something that has got to happen in my view... I don't want to see the American people voting for the lesser of two evils...

You are not allowed to place the definite article before a comparative. But, there are some exceptions, one of which is using it when you compare only two items as in the above examples.

1. You can omit "candidate" after the stronger as it is repeated. The "the" is modifying candidate, not stronger.

2. In "the lesser (evil) of two evils", the "the" modifies the omitted "evil", not "lesser".

In view of this grammatical pattern, there is no reason not to use the indefinite article in your examples as long as we can assume that a noun has been omitted.

Using the indefinite article seems to depend on how you perceive the plural noun phrase. "It has been amazing two months" could be used if you don't perceive two months as a single unit in the same way as in "Two months have passed since he died." The same argument can be made when deciding a subject-verb agreement after the dummy subject there. It depends on how you perceive the subject.