(1) He is more clever than rude.
(2) ??He is as clever as rude.
I've learned (1) is natural and that (2) isn't.
(1) means "He is clever rather than rude".
Then, why can't (2) mean (2b)?
(2b) He is clever as he is rude.
In other words, why is (2) unnatural when (2b) is natural?
The question used to ask why (2) is ungrammatical, but people here seem to agree that (2) is grammatical but just might be unnatural in Present-day English.
- I'd like to know why (2) is unnatural, not whether it's unnatural.
- Also, how natural (1b) is and why?
(1b) He is more clever than he is rude.
The Cambridge Grammar (p 1121) says this is grammatical:
(3) Ed is more old than middle-aged.
and that this is not (p 1122):
(3b) *Ed is more old than he is middle-aged.
So, the Cambridge Grammar specifically says that the insertion of he is in (3) is what makes it ungrammatical.
BTW, the book calls this construction metalinguistic comparison.