If the rule is "such (a) + adj. + noun", why is "such fun" correct?

According to my Cambridge Grammar of English, 'such (a)' is used in noun phrases with attributive adjectives.

She's such a quiet girl. (such a + adjective + singular countable noun)

They're such nice kids. (such + adjective + plural countable noun)

She always uses such fresh food. (such + adjective + uncountable noun)

And indeed, those are the rules as explained in the manual I use: such (a) + adj. + noun. But then, out of nowhere there's this exercise that requires the answer:

It was such fun for all of us to be together.

There is no adjective, and unfortunately no explanations either. So why is that structure acceptable? Or is it just a 'freak exception'?

Solution 1:

This usage of such as an intensifier is both an adjective and adverb:

adj. 2b. Of so extreme a degree or quality: never dreamed of such wealth.

adv. 1. To so extreme a degree, so: such beautiful flowers; such a funny character.

As such, it can modify either a noun (“such fun”) or an adjective (“such nice kids”).

Solution 2:

Such can be used like this:

1. such + a/an + adjective + singular noun e.g. such a nice day
2. such + adjective + plural noun e.g. such interesting magazines
3. such + adjective + uncountable noun e.g such excellent advice

These are the three most common examples of the way we use such. In each example such intensifies the adjective.

However we can also say: He was such an idiot. (such + a/an + noun) And.. such wealth, such a headache. Here we are using nouns which can be graded or which are judgemental. So we don't normally say 'such cars' for example unless it is part of this structure: such cars as these or... such methods as necessary in which case the meaning changes to 'of this type'. Hope this helps.

Solution 3:

The main question you need to ask is whether or not the target of such is countable:

It was such fun for all of us to be together.

Here, fun is not countable so no a is used. However, if you change the sentence above to refer to something that is countable, you will need to add an a (not the most elegant of sentences but it wiill serve as an example):

It was such a fun afternoon we all spent together.

"Fun afternoons" are countable, you can have one, two or many of them, hence the a.

Solution 4:

I think originally people would have said: "It was so much fun for all of us".

In time people substituted "much" with "such" (they sound similar) leaving out the intensifier, so. Grammatically speaking. the phrase "such fun" is wrong as is "so fun" but both forms are becoming increasingly common so we accept it unquestionably.

As for such being used to modify a noun that is not always true. We don't say: "Today was such a day, we went swimming." It makes no sense whatsoever. But we do say: "It was such a delight to stay at..." or "...such a pleasure to meet you." Likewise it's possible to say: "I've got such a headache now!" :)