I know that the noun "correction" is both countable, meaning a change that makes something more accurate than it was before, and uncountable, meaning the act or process of correcting something. When I want to say, "Any correction is appreciated," should I say "any corrections', or are they both correct? Here, I'm referring to my correcting a friend's essay.
The short answer is yes, both are accepted.
The difference is that when saying any correction is appreciated, you can expand it to any act of correction is appreciated.
Any corrections are appreciated, on the other hand, can expand to any number of corrections is appreciated.
Yes, both are correct.
That's because the word any can refer to one or more things i.e. singular and plural.
This said, any correction would mean one time/single correction and making it plural means more than one corrections.
They are interchangeable unless you are peculiar about the number of correction/s.