Learn Hardcore Russian: Я бегу домой, потому что идёт дождь.

бежать (я бегу, ты бежишь…) – one specific, directed action, usually right now or on one occasion.
бегать (я бегаю, ты бегаешь…) – repeated, habitual, or multi‑directional running.

In this sentence, you mean I’m running home right now, one concrete action with a clear direction (home), so Russian uses я бегу.

If you said я бегаю домой, it would sound like I (generally) run home (as a habit) – e.g. every day after work, not this one occasion.

Does я бегу mean “I run” or “I’m running”?

It can correspond to both, depending on context, because Russian has only one present tense form here.

In this sentence, with a clear current reason (потому что идёт дождь), it’s understood as I’m running home (right now).
In a more general statement, я бегу could be translated as I run if the context makes it sound like a planned or narrative action.

English splits this into simple (I run) and progressive (I’m running); Russian doesn’t. Context does the job.

Why is there no word for “am” in я бегу?

Russian does not use the verb быть (to be) in the present tense in normal statements.

English: I am running.
Russian: Я бегу. (literally: I run)

The idea of am is simply included in the verb ending -у in бегу, which already tells you 1st person singular, present.

You only use forms of быть in the past (я был / я была) and future (я буду), not in a simple present like this.

Why is it домой and not дом or дома?

These three are related but different:

домой – to home / homewards (direction, where you are going)
дома – at home (location, where you are)
дом – a house / home as a noun (object, not adverbial)

In я бегу домой, the important idea is movement towards home, so Russian uses домой.

Compare:

Я дома. – I am at home.
Я иду домой. – I am going home.
Я вижу дом. – I see a house.

Could I say я бегу дом instead of я бегу домой?

No, я бегу дом is incorrect.

Домой is a special adverb of direction that you must use for to home.
You can’t just put дом after the verb to mean homewards.

Correct options:

Я бегу домой. – I’m running home.
Я бегу к дому. – I’m running towards the house (more literal, to the building).
Я бегу в дом. – I’m running into the house (emphasis on entering).

But я бегу дом is not grammatical.

What is the difference between домой, к дому, and в дом?

All three involve movement toward дом, but the nuances differ:

домой – general homewards, not stressing the building or entrance, more like to home as a place.
к дому – toward the house; focuses on approaching the house from outside, not necessarily going inside.
в дом – into the house; emphasizes entering the interior.

In everyday speech, домой is the natural choice for going / running home as your destination:
Я бегу домой sounds like I’m going (back) home, not just to a specific building.

Why is it идёт дождь and not something with “it”, like “оно идёт дождь”?

Russian weather expressions are usually impersonal:

Идёт дождь. – literally goes rain, meaning It is raining.
Дует ветер. – Wind is blowing.
Светит солнце. – The sun is shining.

Russian does not use a dummy subject like English it for weather.
The noun дождь itself is the subject; идёт is the verb.

You must not add оно here; оно идёт дождь is incorrect.

What does идёт literally mean, and why is it used with дождь?

Идёт is the 3rd‑person singular of идти – to go, to walk.

Literally, идёт дождь is like the rain goes or the rain is going, but in Russian this is a standard idiom meaning it is raining.

Similarly:

Идёт снег. – It’s snowing.
Идёт град. – It’s hailing.

So while you can think of the literal meaning (to go), with weather it’s best to just learn идёт дождь = it’s raining as a set phrase.

Why is it идёт дождь, not дождь идёт? Is the word order fixed?

Both идёт дождь and дождь идёт are grammatically correct.

Идёт дождь. – neutral, very common for It’s raining as a general weather statement. The verb comes first, which is typical in impersonal‑feeling weather phrases.
Дождь идёт. – possible, but sounds a bit more like you’re emphasizing дождь (the rain), e.g. in contrast to something else.

In everyday speech about the weather, идёт дождь is the standard default wording.

What is the difference between потому что and поэтому?

Both express cause and result, but they work differently in the sentence:

потому что – because (introduces the cause clause)
- Я бегу домой, потому что идёт дождь.
  I’m running home because it’s raining.
поэтому – therefore / so (introduces the result clause)
- Идёт дождь, поэтому я бегу домой.
  It’s raining, so I’m running home.

So:

[Result], потому что [Cause].
[Cause], поэтому [Result].

In your sentence, you’re stating the result first, so потому что is the right choice.

Is the comma before потому что always necessary?

Yes, in this kind of sentence you must put a comma before потому что, because it introduces a separate clause (идёт дождь).

Я бегу домой, потому что идёт дождь. – correct.
Я бегу домой потому что идёт дождь. – incorrect in standard writing.

In Russian, conjunctions that introduce subordinate clauses (like потому что, когда, если) are usually preceded by a comma when they join two clauses.

Can I drop я and just say Бегу домой, потому что идёт дождь?

Yes. In Russian, the subject pronoun is often omitted when it’s clear from the verb ending.

Я бегу домой, потому что идёт дождь.
Бегу домой, потому что идёт дождь.

Both mean I’m running home because it’s raining.

The form бегу already shows 1st person singular, so я is optional and often dropped in spoken or informal language when the subject is obvious.

What is the aspect of бежать and идти, and would побегу / пойдёт work here?

Both бежать and идти are imperfective verbs of motion, focusing on the process:

я бегу – I am in the process of running.
идёт дождь – it is (in the process of) raining.

Their common perfective partners are:

побежать – to start running, to run (as a completed event).
пойти – to set off, to start going.

In your sentence, you are describing what is happening right now, so the imperfective is natural.

Я побегу домой – I will start running home / I’ll run home (future, or stressing the start).
Пойдёт дождь – it will start raining.

So побегу and пойдёт don’t fit here, because the English meaning given is present: I’m running home because it’s raining.