In these sentences, where is the 'noun'?

Question

When I study English, I often come across this kind of pattern that I think is a bit awkward. These two sentences are written on my textbook.

1. Western dishes are probably still the most popular.

2. It's the most beautiful when the foliage changes into all different colors in the fall.

I know adverb 'most' back up the adjective 'popular' and 'beautiful'. Then, how about 'the'?

I think when I need to use definite article 'the', there have to be a noun somewhere that goes with 'the'. However, there's no noun anywhere that 'the' is used together with. So, what if I leave 'the' out or add noun to existing sentence?

1a. Western dishes are probably still the most popular ones.

1b. Western dishes are probably still most popular.

2a. It's the most beautiful time when the foliage changes into all different colors in the fall.

2b. It's most beautiful when the foliage changes into all different colors in the fall.

Answer 1

First of all, there's nothing wrong, or even odd, about #1. [western] Dishes are [the] [most] popular. There's a noun subject, and a predicate modifier. With or without the square-bracketed words it is a complete sentence. As for the use of "the", it acts as an intensifier, making a (unique) superlative. popular->more popular->most popular ->THE most popular.

Number 2 is a different beast entirely. As you noticed, the pronoun "it's" doesn't really refer to anything. Or rather , it points forward to whatever the rest of the sentence means. There's an official linguistic name for such usage of "it's" or "there's", but let's just call them placeholders. Depending on context, "it" might refer to "Vermont" or some town. In that case you wouldn't need to reinterpret or rephrase at all to make sense of the sentence. But even supposing "It's" is indeterminate, a placeholder—#2 is still grammatically correct. However, so are both your phrasings. 2b) is a slightly less emphatic rendering. But adding "time", as you did in 2a)—although it might please your ear and grammatic sensibilities to have a noun to go with "beautiful"— might not be true to the original intent. Because you are assuming what "it" is. You could have just as easily inserted "place", which you see would change the meaning in another direction. So, even though the sentence is vague, it is not wrong, and changing it by adding some word will make it more specific, but not necessarily better.

Answer 2

Popular and beautiful are functioning as nouns here. It is quite common to use adjectives as nouns.

Youtube: Only the good die young
imdb: The good, the bad and the ugly

Merriam-Webster has an explanation about this use:

A lot of these kinds of adjectives can be found in titles of works. The title of Norman Mailer’s novel The Naked and the Dead contains two adjectives that are essentially functioning as nouns. The same goes for Stendhal’s The Red and the Black and F. Scott Fitzgerald’s The Beautiful and Damned. Consider also the Martin Scorsese film The Departed or the American TV soap opera The Young and the Restless.

In order to understand the sentences, yuo can imagine a "missing" nouns like ones, people, things, etc, but these nouns are, in natural speech, not actually added.

What happens in your (b) versions of the sentences, is that you change the meaning: xyz is most beautiful uses the superlative to mean very.

Western dishes are probably still most popular.
means: Western dishes are probably still very popular.

Compare to expressions like

Oh, the information you gave me was most useful!

I'd say this kind of use of the superlative may come over as slightly dated, but most importantly, it doesn't literally mean the most xxx!