Learn Hardcore Russian: Если кто‑нибудь позвонит, скажи, что я вернусь позже. - If someone calls, say that I will come back later.

In English:
If someone calls, tell them I’ll be back later.
The if‑clause uses present, but it refers to the future.
In Russian, when the condition refers to a specific future situation, you normally use future tense in the если‑clause:
- Если кто‑нибудь позвонит, скажи…
  Literally: If someone will call, say…

Using если кто‑нибудь звонит would sound like you are talking about a habitual situation (e.g. “If someone calls (in general / usually), he always asks for you”), not a single future event.

So: future in Russian если‑clause ≈ present in English if‑clause when speaking about a specific future event.

Why is позвонит perfective and not звонит or будет звонить?

Russian aspect matters a lot here:

позвонит – perfective, future (he/she will call once; the act of calling will be completed).
будет звонить – imperfective future (will be calling / will keep calling / will be in the process of calling).
звонит – imperfective present (is calling / calls), used for present or habitual actions.

In this sentence we care about the fact of a single call happening (and being completed), not about a process or repeated action. That is why позвонит is the natural choice.

Compare:

Если кто‑нибудь позвонит, скажи… – If someone calls (once), tell them…
Если он будет звонить, не бери трубку. – If he keeps calling / is going to be calling, don’t pick up.

What is the difference between кто‑нибудь, кто‑то, and кто‑либо?

All three mean roughly “someone / anyone”, but they differ in nuance and typical use:

кто‑нибудь
- Very common, neutral.
- Often means “someone (unspecified)” or “anyone”.
- Works well in questions, conditionals, and contexts where you really don’t care who it is:
  - Если кто‑нибудь позвонит… – If someone / anyone calls…
кто‑то
- Slightly more concrete: “somebody (particular but unknown)”.
- Often suggests that there really is or will be such a person:
  - Кто‑то звонит. – Somebody is calling (you can hear the phone).
кто‑либо
- More formal, often used in official / written style, or in negative contexts with ни (like никто, никогда).
- In colloquial speech you’d usually pick кто‑нибудь or кто‑то instead.

In this sentence, кто‑нибудь is natural: we don’t care who calls; it’s just anyone.

Why is there a hyphen in кто‑нибудь?

Indefinite pronouns like кто‑нибудь, что‑нибудь, где‑нибудь are written with a hyphen in Russian spelling.

So:

кто‑нибудь – someone, anyone
что‑нибудь – something, anything
где‑нибудь – somewhere, anywhere

It’s just an orthographic rule: the particle ‑нибудь is attached with a hyphen to the interrogative word (кто, что, где, etc.). The same is true for particles ‑то, ‑либо, ‑нибудь:
кто‑то, когда‑либо, как‑нибудь, etc.

What exactly does если mean here? Is it more like “if” or “when”?

Basic meaning: если = if.

In context, Если кто‑нибудь позвонит… can sometimes be translated as either:

If someone calls, tell them…
When someone calls, tell them… (if the call is expected)

Russian если itself doesn’t distinguish between if and when the way English sometimes does. The context (is the call likely? expected?) decides whether if or when sounds better in English.

But grammatically, если is the standard word for if in conditionals.

What is скажи and how is it formed?

Скажи is the informal singular imperative of сказать (to say / to tell).

Infinitive: сказать
3rd person singular future: он скажет – he will say
Informal tell! / say! (to one person): скажи
Polite / plural tell! / say!: скажите

So:

Скажи, что я вернусь позже. – Tell (you, friend) that I’ll be back later.
Скажите, что я вернусь позже. – Tell (you all / you, politely) that I’ll be back later.

This sentence assumes you’re speaking to one person informally.

Why is что used here? What does скажи, что я вернусь позже literally mean?

Here что is a subordinating conjunction introducing an indirect statement, similar to English “that”:

скажи – say / tell
что – that
я вернусь позже – I will return later / I’ll be back later

So literally:

Скажи, что я вернусь позже.
→ Tell (them) that I’ll be back later.

Just like in English, you could sometimes drop “that” in translation (Tell them I’ll be back later), but in Russian что normally stays.

Why is it я вернусь, not я возвращусь or я буду возвращаться?

There are two main verbs:

вернуться – to return, to come back (perfective, usually one‑time, result‑focused)
возвращаться – to return, to be returning (imperfective, process / repeated / habitual)

In normal modern speech, я вернусь is the standard way to say “I’ll be back / I will come back” in this context.

я вернусь позже – I’ll be back later (one event, focus on the result: I will have come back).
я буду возвращаться позже – I’ll be returning later (more about the process or repeated, sounds strange here if you just mean one return).
я возвращусь exists but is much less common and can sound bookish or dialectal in many regions; я вернусь is the default.

So я вернусь позже is the natural, idiomatic choice.

What aspect and tense is вернусь, and how is its future formed?

Infinitive: вернуться (perfective)
1st person singular future: я вернусь – I will return

Perfective verbs in Russian form a simple future by using present‑tense endings:

прочитать → я прочитаю – I will read (finish reading)
написать → я напишу – I will write
вернуться → я вернусь – I will return

So вернусь is:

Perfective
Future tense
1st person singular (I)

Imperfective возвращаться would form a compound future:

я буду возвращаться – I will be returning / I’ll be in the process of returning.

Why is there a comma before что, and also after позвонит?

Russian comma rules here:

Если кто‑нибудь позвонит, скажи…
- This is a complex sentence with a subordinate clause.
- Если кто‑нибудь позвонит is a conditional subordinate clause.
- скажи… is the main clause.
- Rule: Subordinate clause is separated from the main clause by a comma.
…скажи, что я вернусь позже.
- что я вернусь позже is another subordinate clause, object of скажи.
- Rule: Subordinate clauses introduced by conjunctions like что are usually separated by a comma.

So the commas mark the boundaries of the two subordinate clauses:

[Если кто‑нибудь позвонит], [скажи, [что я вернусь позже]].

Can the word order change? For example, can we say Если позвонит кто‑нибудь or скажи, что вернусь позже?

Yes, Russian word order is fairly flexible, though it can affect emphasis.

Если позвонит кто‑нибудь, скажи…
- Grammatically fine.
- Slight emphasis shift: позвонит (the act of calling) comes first.
- Neutral если кто‑нибудь позвонит is more common, but both are acceptable.
Скажи, что вернусь позже.
- Dropping я is possible in casual speech, because the subject “I” is understood from the verb ending ‑усь.
- It sounds slightly more informal:
  - Скажи, что вернусь позже. – Tell them I’ll be back later.

So both Если позвонит кто‑нибудь… and скажи, что вернусь позже are acceptable variations, especially in spoken Russian.

How would this sentence change when speaking politely or to more than one person?

The main change is the imperative form of сказать:

To one person, informally (ты):
- Если кто‑нибудь позвонит, скажи, что я вернусь позже.
To one person politely (вы), or to several people:
- Если кто‑нибудь позвонит, скажите, что я вернусь позже.

Everything else in the sentence can stay the same; just choose скажи (informal singular) or скажите (formal/plural) depending on whom you are addressing.

Can we say позже in other ways? What is the difference between позже, попозже, and позднее?

All three can translate as “later”, but they have nuances:

позже
- Neutral, most common:
  - Я вернусь позже. – I’ll be back later.
попозже
- Slightly more colloquial; often means “a bit later / somewhat later”:
  - Я вернусь попозже. – I’ll be back a bit later.
позднее
- More formal or bookish, sometimes used in written style or news:
  - Я вернусь позднее. – I shall return later. (formal tone)

In this everyday sentence, позже is the most typical choice.