why do we need to study english?

(As a side note, I don't think "Keep (subject optional) ______" is not really a thing. Leaving out the subject just means that the imparative "you" takes the role of the subject. "Keep quiet" is "You keep quiet")

I'm not sure what point you're trying to get at with all those double negatives exactly, but I meant it more in the specific context of this exercise. (Also back-editing this post it was a badly phrased question brought upon again by Shit Grammatically Going Off Around Me I Take For Granted As A Native English Speaker)

I had to go look this up but yeah, for who knows what fuckin reason when you've got an imperative sentence in English it often drops the subject pronoun. Which is why some adjectives work fine because they're congruent with state-it's-reasonable-to-ask-a-human-listener-to-maintain (quiet, warm) but others sound weird unless you add a subject/pronoun after "keep" to clarify. (Keep him busy, keep the radio on, keep your afternoon free, keep the ingredients cool, keep your essay topic specific, keep your rate of talking slow.).

Then there's a bunch of other shit which I don't think ever fits simply because it's physically impossible for the imperative'd listener to work to keep the subject in its requested state. In what context (or with what <something>) could one "Keep <something> expansive", or "Keep <something> rich"?

It was more like "which adjectives work proceeding keep? Do some work ok just as keep <adjective> but do others need some kind of subject added in there? Why/how the heck?"

Conversely Keep precedes verbs (like "Keep trying" "Keep walking" "Keep being <human-congruent adjective>") with much less fuss so I'm much less vexed by those.

Also I forgot to mention this earlier but please don't use the word "Engrish" in this thread again. Or just in general, Thanks