What is the meaning of "за" in expressions relating to time?

Question

More specifically, what is the difference in meaning between:

Анна: Сколько времени ты делала домашнее задание?
Нина: Я делала домашнее задание час.

and

Анна: За сколько времени ты сделала домашнее задание?
Нина: Я сделала домашнее задание за час.

Is there any significance to the fact that perfective verbs are only used with "за" and that imperfective verbs are only used in the absence of "за"?

Background information: This relates to Exercise 91 on page 134 of the German version of this workbook and the two examples preceding it. (See here.)

The only result I could find discussing this using Google was this. However, it does not seem to address the specific situation I am confused about ("за сколько времени/сколько времени" as well as "за+(винительный)срок/(винительный)срок").

Also, the answers seem to imply that there is a difference in meaning between: "Как долго она не работала?" and "Сколько времени она не работала?", which would be very confusing to me, since Exercise 87 on page 133 and the preceding example of the same workbook would seem to imply that there is no difference between them. If there is actually a difference, I could ask that as a separate question, I just wanted to explain why I found the thread on WordReference unhelpful.

Answer 1

Yes, you (and shabunc) are right that aspect is involved here. To use English for comparison:

за + (time period) + perfective verb expresses how long it took to complete or accomplish something.

Я прочитал книгу за неделю.
I read the book in a week/It took me a week to read the book. [and I've finished it]

Using just the time period in the accusative, with an imperfective verb, expresses duration: how long you spent on an activity, with no indication of whether you completed it, or whether there's a result.

Я читал книгу неделю.
I read the book for a week/I spent a week reading the book. [no indication of whether I finished it or not; maybe I gave up on it after a week. I'm just stating how long I was reading it.]

Answer 2

William

I'll try to answer your questions from another perspective.

"Also, the answers seem to imply that there is a difference in meaning between: "Как долго она не работала?" and "Сколько времени она не работала?"

Despite there's difference in form, the meaning is just the same.

And your another question:

"Is there any significance to the fact that perfective verbs are only used with "за" and that imperfective verbs are only used in the absence of "за"?"

I'd say, there's no significance to this fact. Let us see the examples:

Анна: За какое время ты сделала домашнее задание? (What time did it take you to do the homework)

Нина: Я сделала домашнее задание за час.

Imperfective verbs can be used with the preposition "за" as well.

Анна: За какое время ты делаешь домашнее задание? (What time does it take you to do the homework)

Нина: Я делаю домашнее задание за час.

"ЗА" in expressions relating to time means either "how much time does/did/will it take" e.g.: За какое время? За какой срок? or "for the time of smth e.g.: За время учебы. За время каникул.

In the situation you are concerned about:

Сколько времени ты делала домашнее задание? vs За сколько времени ты сделала домашнее задание? Both the preposition "За" and a perfective aspect are used to highlight that the action is finished. But they are translated in the same way into English: How much time did it take you to do your homework?

And, also, probably some knowledge of aspect will help you investigate this puzzle. (I suppose, you already know that, but, to my mind, it never hurts to revise). As well as in English, there are two aspects: perfective and imperfective.

Imerfective aspect has three tense forms:

(all of them are used when talking about incomplete actions)

1. The past form: Я делал /Eng: I did

2. The present form: Я делаю /Eng: I do/I am doing (and here it probably gets tricky)

3. The Future form: Я буду делать /Eng I will do

Perfective aspect has only two forms:

1. The past form: Я сделал /Eng: either I did smth or I have done smth (BUT in Russian it's never about Present, in other words, it is NEVER about duration from the past until now. It is always about actions in the Past. This form is used when talking about completed actions)
2. The present form: Я сделаю /Eng: I will have done it (it is always about the result in Future) It is tricky, because there's a present form, but a Future meaning. And again, we are takling about completed actions.

Hope that helps

Answer 3

Well, as you can see, in the given context both "сколько [времени]" and "за сколько времени" are corresponding to the phrase "how much time" in questions like "how much time it will take".

But actually, William, your observation is quite elegant and, the most important, valid. This is indeed has something to do with the perferctiveness/imperfectiveness of Russian verbs.

This is even more obvious when we are talking about some actions that yet to be done, probably in future (if they are supposed to be done at all).

Compare following pairs of questions:

• Сколько [времени] ты ещё будешь собираться!
• За сколько [времени] ты соберёшься.

or

• Сколько ещё времени ты будешь делать домашнее задание?
• За сколько времени можно сделать домашнее задание?

See, whenever we have so-called "будущее несовершенное" - one that is used with "быть" - "сколько" is used, and with "будущее совершенное" (future perfect) or just infinitive of a perfect verb "за сколько" is used.

As a sidenote, just to mention, there is a separate colloquial "Сколько времени?" which has a different meaning - "how much time it is?"