In the sentence " They want me to do this sober ", why is an adjective being used to describe a verb ( do )? [duplicate]

In a movie, the interviewer wanted to interview someone, and then his friend offered him a drink, but the interviewer said " They want me to do this sober ". "They" refers to his bosses.

Shouldn't he say "soberly" instead of "sober" ?

Thanks in advance

Solution 1:

In the sentence " They want me to do this sober ", why is an adjective being used to describe a verb ( do )?

It isn't. "Sober" is an adjective: It is not a flat adverb (if such beasts exist.)

"They want me to do this sober" = "They want me to do this whilst I am sober."

The "whilst I am" has been omitted. Of course, "whilst I am sober." is adverbial but "sober" itself, is not.

Edit: I had missed the post by Anthony Grist when I answered. I see that this is practically a repeat.

Solution 2:

As commented by @Anthony Grist below the question...

He's using the not affected by alcohol; not drunk meaning of sober, not the serious, sensible, and solemn meaning. The adverb soberly only has a meaning that corresponds to that latter definition for sober (in a serious, sensible, and solemn manner).
A lot of actual usage of English omits words; what the speaker means is They want me to do this while I'm sober, but they've dropped the while I'm part.

I can't see anything useful to add to that.