Only use "higher" for something that could be described as "high" in the first place.
It is incorrect to say "The CEO earns high," so there is no way to use "higher" correctly in such a sentence.
It is correct to say "The CEO's salary is high" or "The CEO earns a salary that is high."
Therefore, the answer to all of your questions below is YES.
ooisuankim wrote:
Do I understand correctly that "higher" cannot modify earns, and therefore can never function as an adverb in a numerical comparison. Hence, the word "twice as much as" is used in this context. [YES] Does it also follow that "twice as high as" is incorrect in this example? For example, will this sentence be incorrect? "The CEO earns twice as high as the average employee at this company" [YES, it is wrong.]
Following on from this, is this sentence construction correct?
"The CEO's salary is twice as high as the average employee at this company" [YES, this is correct.]
Thank you.