novice posted:Concerning sentences 3 and 4, the reason why they are ungrammatical is that they are not parallel, isn't it?
As I observe, in the first part, the action verb "destroy" is used, but in the other, the verb "be" is used. So, they are not parallel.
Please note that "sentences 3 and 4" is misleading, because there are no sentences here with such helpful labels. I assume you mean to refer to the the third and fourth sentences in my previous quotation of you:
(3) The more we destroy forests, the more natural disasters are.
(4) The more we destroy forests, the more are natural disasters.
If the reason they don't work is that the same verb isn't used in both parts of the sentences, why do you think I recommended changing "are" to "happen" or "occur" in (3)? Clearly it wasn't to match the verb in the first part ("destroy").
The reason you can't say "the more natural disasters are" is that "Natural disasters are (the) more" doesn't work as a sentence. Your use of inversion in (4) then takes what's bad and makes it even worse.
But, as I said before, if you want to use "are" rather than "occur" or "happen," you can simply add existential "there." Just as we can say, "There are more natural disasters," we can use "the more there are natural disasters." ♣