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

I.       In your first example, Я открываю окно would translate into Present Continuous: I am opening the window.

Я открою окно has a meaning of a Future Tense, or intention: I am going to open the window. Those two phrases can have same or different meaning, depending on the contents, in exactly the same way both in English and in Russian. Compare: 

1. Same meaning:   It is too hot here; I am opening the window. OR: It is too hot here; I am going to open the window. (Жарко, я открываю окно. ИЛИ: Жарко, я открою окно.)

2. Different meaning:- What are you doing? - I am opening the window. OR: I am going to open this window as soon as it gets warm outside. ( - Что ты делаешь? - Я открываю окно. ИЛИ: Я открою это окно, как только потеплеет.)

II.   Открывать and Открыть bear the difference between Indefinite and Perfect in English. Открывать is incomplete action, and Открыть – complete. 

Я открывал и открывал эту задвижку, пока не открыл.

I kept opening and opening this latch until I had opened it all the way.

I would agree with your example of more urgency in Открывай vs Открой. I will try to illustrate it with the translation:

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

*Open that Door!* (pause) *Open it!* (pause) *Start opening it now, damn it!*

III. The last one.  

Нельзя открыть окно has the meaning of technical obstruction: you cannot open the window because it is nailed closed.

Нельзя открывать окно has a meaning of prohibition. You are not allowed to open the window.