Американец просит совета в изучении русского ⇐ Морфология

[Nano9]

Помогите мне помочь ему объяснить =)

My understanding(or assumption), which may contain many mistakes, is below and let me have your comments when you feel fine ( I understand you are sick now.....)

It is about the use of an imperfective imperative in relation to an expected action (or заранее известное действие).

A group of imperfective verbs match expected actions better than
non-expected actions (new events as fresh news).

For example:

If none of the students think about the opening of windows,
the teacher should say, "Откройте окна!" not "Открывайте окна!".

If the students think it is quite natural to open the window,
the teacher may say "Открывайте окна!" as well as "Откройте окна!".

It is natural to use the imperfective "Открывайте" for an expected action.
It is more or less unnatural to used the imperfective "Открывайте" for an action which is not anticipated.

The exception is the case in which an action urgently required.
"Открывайте окна срочно! Ядовитый гас!".

The perfective is a result oriented verb, whereas the imperfective is
an action (process) oriented verb although the imperfective can
practically express the completion of an action..

There are another group of verbs which can be used regardless of
whether their targets are expected actions or not.

For example:
"Вставай! Уже восемь."
Such verbs are Ужинай!, Завтракай! etc.

I assume the actions these verbs express are customary in life so they
are thought to be always expected actions.

Please note that my concern is about the use of an imperfective for a
"single" action.

The imperfective may express
1) Continuing action
2) Repeated action
and
3) Single action like "Вставай! Уже восемь."

As far as I know, 3) Single action is not explained in Russian grammar
books for foreign learners published in Russia .