Are "[не]долго", "[не]надолго", and "[не]давно" interchangeable?

Question

1. What's the difference between долго and надолго (and also недолго and ненадолго)? They both seem to mean for a long time. Any practical/grammatical difference, or can I just use them interchangeably?

2. When used with the present tense, what's the difference between долго and давно?

both

Он давно живёт в этом доме.

and

Он долго живёт в этом доме.

seem to mean He's been living in this house for a long time.

Also - last thing, RT gave the examples of:

Он долго не звонит мне.

AND

Мы давно не были на море.

What's the difference between using these two expressions of 'for a long time something hasn't happened'.

Thanks a lot for any help - I know I overloaded a little with Qs.

Answer 1

I'll try to offer a slightly more "formalistic" explanation.

• "Долго" refers to a long stretch of time. How long, and up to which point, depends on the context.

  "Недолго" is a short stretch of time.

  • "Надолго"/"Ненадолго"¹ is for that stretch of time, and usually expresses intention.

• "Давно" is a point in time long in the past.

  "Недавно" is a recent point.

  • In practice, especially in negative sentences and/or in present, "давно" implies since that point, and thus is semantically similar to "долго".

Let's make examples. Some of them will be less commonly used, but they all work.

Он долго живёт в этом доме

He lives in this house for a long stretch of time [up to now, because it's in present].

Он давно живёт в этом доме

He lives in this house since long in the past [and up to now].

The meaning is indeed very similar, if not identical. But let's turn it into past:

Он долго жил в этом доме.

He lived in this house for a long stretch of time [but doesn't now].

Он давно жил в этом доме.

He lived in this house at some point long in the past [i.e. long time ago]. [And he doesn't for a long time already].

Now the difference is substantial.

Let's use "надолго". "Надолго живёт" doesn't work well together, because the word implies intention, but we can use it like that:

Он надолго поселился в этом доме.

He settled in this house and intends to live there for a long time.

A very blunt example:

Это было давно.

It happened long time ago.

Это было долго.

It lasted a really long time.

Это надолго.

This is [here to stay] for a long time.

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¹ There are two slightly different expressions "ненадолго" and "не надолго". Let's leave it for another time. Also, logically, "на недолго" should exist, but it doesn't.

Answer 2

Short answer: they are not interchangeable, for grammatical as well as semantic reasons. Let's start with 2)

давно is "long time ago" (Он давно жил здесь) or perhaps "since long time ago" (Он давно живет здесь) and not "for a long time". Now, it doesn't work with negative sentences in English, but it does in Russian. Moreover,

я давно был на море

и

я давно не был на море

have similar meaning: I was at sea a long time ago. But negative sentence has this additional aspect of "and I haven't since then".

Here you can use "я долго не был на море" with almost the same meaning. But this sort of implies that the situation has changed. Я долго не был на море - I haven't gone to sea, but now I am here or is going to. Я давно не был на море - I haven't gone to sea and perhaps I will never go, or perhaps I will, it's unknown

I will use your examples with slight changes

Он долго не звонил мне

He hasn't called me fоr a long time (and then he did). We don't know whether he called before

Он давно не звонил мне.

He called me in the past. Then he hasn't called me for a long time. (and perhaps he is still not calling me)

Now for 1) долго is used with verbs of perfective aspect (? совершенного вида) and надолго is used with verbs of imperfective aspect (? несовершенного вида). That's from grammar point of view. Semantically it's a bit more complex - can't do it from the top of my head. I will just give some sample sentences

Я долго сидел за компьютером

I was sitting behind my comp for a long time. (Not anymore). It's a factual description

Я надолго сел за компьютер

I've sat behind my comp and it's going to be for a long time. More like a matter of intention.