In the following sentences:
- I can move quicker than she can.
- She moves quickly, but I can move quicker still.
- Between us, I move quickest.
- Between us, I move quicker.
- I am even quicker than she.
I am apparently trying to modify the verb "move" with the adjectives "quicker" and "quickest".
It seems to me that I have been speaking like this all my life, but just now I've been told that adjectives may not modify verbs, and that these sentences are grammatical garbage. Yet, when it comes to:
I can move quicker than she can.
vs
I can move more quickly than she can.
The first sentence sounds just as good as the second, to me, at least. Cannot the word "quicker" serve as both adjective and adverb?