Adding “the” before the noun in correlative comparative structure.

Interesting question, Meriem.

@Meriem posted:

STRUCTURE A: The more + adjective + noun + …

(1) The higher (the) level you reach, the easier it is to speak English.

(2)  The longer (the) hours you work out, the stronger you become.

(3) The hotter (the) weather is, the more you sweat.

(4) The smaller (the) car is, the less petrol it uses.

(5) The more you earn, the more expensive (the) things you buy.

(6) The fewer (the) students, the more I like the lessons.

(7) The older (the) people, the wiser they become.

Yes, you need "the" in sentences (1) to (7).

@Meriem posted:

STRUCTURE B: The more + noun + …

(A) The more (the) fruits you eat, the more (the) vitamins you get.

(B) The more earlier you leave for work, the more (the) tasks you complete.

(C) The more you study, the less (the) time you have for friends.

(D) The more (the) rules we know, the more correctly we write our tests.

The double comparative in sentence (B) is ungrammatical. You should say "the earlier."

You don't use "the" in sentences (A) to (D) because "more" and "less" do not work well in predicative position.

While we can say things like:

1a. As the level you reach is higher, it is easier to speak English.

for sentences (1) to (7), it sounds unnatural to find "more" and "less" after the copulative verb:

Aa. ?As the fruits you eat are more, you get more vitamins. (Also, I prefer the singular: The more fruit you eat, the more vitamins you get.)

In conclusion, I think "be" needs to be implicit (or explicit) in these structures for "the" to be used.

Thank you for your time. That was helpful.