I'd like to note (and confirm) the following (inconsistency):

  1. Equations (3) and (4) are complex.

  2. The 3rd and 4th equation are complex.

The full version of the sentences:

  1. Equation (3) and equation (4) are complex.

  2. The 3rd equation and 4th equation are complex.

I was told the reason that it was singular in the second sentence was due to the intention of the full version in fourth sentence. Same logic, though, doesn't apply to the first sentence.


I changed the sentences from 'fine' to 'complex' not to confuse when someone says that the sentence is fine. I'm also adding more details since there might be a disagreement in the comments about the second sentence--that is should be equations and not equation.

It all started here:


The surfers example isn't good since beginner isn't an adjective, but you get the idea.

Back then, I asked Neil about it and he said:

It should be singular in the case when you use the definite article in front of the adjectives.

"He fed a small and a big dog."

There is an elision of a word in that sentence [* elision doesn't seem to refer to this; maybe whiz deletion?], which is fine in English. It is shorthand for "He fed a small dog and a big dog." You can omit the first instance of the noun and still be OK but you do not pluralize the remaining instance.

But the indefinite [* I think he meant definite] article or no articles require a plural:

He fed small and big dogs.

He fed the small and big dogs.

He fed the small and the big dogs.

He fed a small and a big dog.

So, in the case in the forum, it should be: We are a beginner and an advanced surfer.

The definite article is what forces the singular noun.

I asked him about two links:



and he added:

There is an overlapping case where either the plural or the singular works, as noted in the first of your examples.

He fed the small and the big dogs -> implies that there is at least one of each

He fed the small and the big dog -> implies there is exactly one of each

He fed a small and a big dog -> implies that there is exactly one of each

He fed a small and a big dogs -> is wrong

I'm still not clear if

He fed the small and big dog.

is okay (implying one of each), and if not why.


Similarly, I'm not sure if I can say:

It involves a technological and theoretical challenge,

where I mean that it involves a technological challenge and a theoretical challenge. It might be confused with involving a single technological, theoretical challenge.


I tweaked a bit the above edits.

I think that even if technically I can use a single in/definite article with a singular noun (describing two objects), due to the risk of confusion (that I made a mistake and used 'and' between two adjectives preceding a noun), I should avoid it.

This puts some doubt on the correctness of the 2nd sentence even though it should be clear that I'm referring to two equations (it's an elision of the 4th sentence) and not a single equation that is both the 3rd and 4th.


Seeking more confirmation since it became convoluted


  • No, the 3rd and 4th equations are fine. The 3rd equation is fine; the 4th equation is fine. Both are fine.
    – Lambie
    May 20, 2021 at 22:27
  • I updated the post.
    – Zohar Levi
    May 21, 2021 at 11:51
  • He fed the small dog and the big dog. = implies he did not feed the medium-sized dog. And: It involves a technological and theoretical challenge. = the challenge is both technological and theoretical. It is a large and airy building. And yeah, I said they were fine before you made it so confusing. Book 2 and Book 3 are not very good. They are taken together.
    – Lambie
    May 21, 2021 at 14:14
  • I think it should be: "It is a large, airy building." You don't put 'and' between a list of adjectives that precedes a noun. I corrected the first edit and removed one 'the.' It's the same case like the challenge. It's probably not advisable to write a singular with definite article exactly due to the confusion with the large, airy building.
    – Zohar Levi
    May 21, 2021 at 22:00
  • If you know, why ask? A large and airy building sits atop the hill. So, you are mistaken.
    – Lambie
    May 21, 2021 at 22:21

1 Answer 1


You have many edits in your question so I may not be able to address everything, but let me try.

Firstly, I disagree that the following sentence is correct:

The 3rd and 4th equation are complex.

This is because the sentence does not follow subject-verb agreement. "Equation" is singular; "are" is not. The sentence should read

The 3rd and 4th equations are complex.

Secondly, you reference being unclear about the sentence:

He fed the small and big dog.

While I don't think there's anything wrong with this sentence, the construction isn't ideal. It happens to work in this case because nothing can be both "small" and "big", but if you have the sentence

He drove the red and blue car.

this causes problems because it is not clear whether it is referring to one car of two colours (red and blue) or two cars, one red and the other blue. If you were going for the latter, as you are in your example sentence, it would be better if the sentence was

He drove the red and the blue car.

Thus, for the sake of consistency, it is probably best to write the sentence as

He fed the small and the big dog.

Thirdly, what I mentioned just now also adds to the confusion surrounding the sentence

It involves a technological and theoretical challenge.

You can probably guess how to fix this - in fact, you wrote it yourself:

It involves a technological and a theoretical challenge.

While this is no more correct than the first sentence, it eliminates the confusion.

  • Did you imply that the problem with the second sentence is that an equation can be both 3rd and 4th unlike a dog which can't be both big and small?
    – Zohar Levi
    Jun 1, 2021 at 9:00
  • By the way, since you mentioned the challenge: if I refer to a single challenge, would you say "a technological and theoretical challenge" or "a technological, theoretical challenge"? english.stackexchange.com/questions/567595/…
    – Zohar Levi
    Jun 1, 2021 at 9:00
  • @ZoharLevi No, an equation cannot be both 3rd and 4th in a list. And when it comes to the challenge, either would be fine, but the latter is less ambiguous.
    – Kman3
    Jun 1, 2021 at 14:56
  • Okay, so I think your answer is inconsistent. First, I assume you are fine with: "The 3rd and the 4th equation are complex." Now, can you explain please why aren't you fine with "the 3rd and 4th equation are complex," but are fine with: "He fed the small and big dog?" It seems that the reasoning that you applied to one hold of the other (whether rejecting or agreeing). Maybe the following would be closer to the target: "The small and big dog are cute."
    – Zohar Levi
    Jun 1, 2021 at 23:00
  • @ZoharLevi As I wrote in my answer, "He fed the small and big dog" is fine, but not ideal. This sentence, however, is different from "The 3rd and [the] 4th equations are complex" because in the first sentence the verb fed does not change regardless of whether you write "dog" or "dogs". In your final example, "The small and big dog are cute", this would have to change to "The small and big dogs are cute" for the reason I gave earlier: dog is singular. Are is not.
    – Kman3
    Jun 2, 2021 at 1:01

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