eat fast/eat quickly

[worcester]

Hello everyone,

1. He always eats fast.
2. Don't eat so quickly!

Are these sentences correct? If they are then can I use "quickly" in sentence N1 and "fast" in sentence N2?

Thank you.

 

[Rover_KE]

Yes to all questions.

 

[Roman55]

I am not a teacher.

You can use them interchangeably because they are both adverbs.

However, as far as what 'sounds' natural is concerned, I think that since "quickly" is only an adverb but "fast" is both an adjective and an adverb they don't feel the same in every situation.

In 1. I would use either, with a preference for "quickly".
In 2. I would use "fast". 2. is an imperative and a short command works better for me.