Imperfective and Perfective Aspects for Non-Personal Moods

Question

The relevance of aspect for the correct usage of verbs seems to be explained only for the personal moods of verbs (e.g. indicative), but what is the meaning of aspect for the impersonal moods, such as the infinitive or the imperative?

To clarify, whereas I can detect a certain difference between Я открываю окно and Я открою окно, I don't understand how one would choose between the two aspects in the imperative. Is there a difference between Открывай! and Открой! ?

I once asked a native speaker about this, and while they acknowledged the two forms to have roughly the same meaning in the imperative, they seemed to think the imperfective implied more urgency of the request. As an example, a person requesting access multiple times would say:

— Открой! (pause) Открой! (pause) Ну открывай же!

But somehow this doesn't quite fit in with my understanding of aspect. Similarly, for the infinitive, what is the difference between Нельзя открыть окно and Нельзя открывать окно?

Answer 1

Similarly, for the infinitive, what is the difference between Нельзя открыть окно and Нельзя открывать окно?

Нельзя in those sentences has different modalities:

• Нельзя (невозможно) открыть окно - you are not able to open the window
• Нельзя (запрещено) открывать окно - you should not attempt opening the window

Physical impossibility to open the window only applies to result (nothing prevents you from trying), that's why we use perfective (state transition) aspect.

Forbiddance only applies to a person (you can't forbid an openable window from being open, only a person from opening it), so we use imperfective (state) aspect.

However, with a positive predicative, this sentence:

• Можно открыть окно?

may mean both "is it possible to open the window?" and "may I open the window?", while this one:

• Можно открывать окно?

may mean only the latter. It implies that the window had been closed for a reason which is no more valid.

Those subtleties of нельзя and можно are so confusing that the use of the words is discouraged in Russian Army:

— Товарищ капитан, рядовой Иванов по вашему приказанию прибыл, можно войти?

— Можно Машку за ляжку, а в армии — "разрешите"!

From the grammar's point of view, it's impossible to tell whether Private Ivanov asked for permission to enter or for physical possibility, that's why the captain told him to clarify his question.