Learn Hardcore Polish: Mój wnuk mieszka teraz za granicą.

moja – feminine singular (e.g. moja wnuczka – my granddaughter)
moje – neuter singular OR non‑masculine-personal plural (e.g. moje dziecko – my child, moje książki – my books)

So:

mój wnuk – my grandson
moja wnuczka – my granddaughter
moje dziecko – my child

What is the grammatical form and gender of wnuk?

Wnuk is:

masculine
singular
nominative case (the “dictionary form”)
animate (it refers to a person)

Basic singular declension of wnuk:

Nominative: wnuk (who? what?) – subject
Genitive: wnuka (of whom?)
Dative: wnukowi (to/for whom?)
Accusative: wnuka (whom?)
Instrumental: wnukiem (with whom?)
Locative: wnuku (about whom?)
Vocative: wnuku! (direct address)

In the sentence, wnuk is the subject (who is living abroad?), so nominative is used.

Why do we use mieszka and not jest to talk about where someone lives?

Polish distinguishes clearly between being and living (residing):

być = “to be”
mieszkać = “to live / reside / dwell (somewhere)”

To say where somebody lives, you use mieszkać:

On mieszka w Warszawie. – He lives in Warsaw.
Mój wnuk mieszka za granicą. – My grandson lives abroad.

If you said:

Mój wnuk jest za granicą.

that would mean “My grandson is abroad (right now / at the moment)”, not necessarily that he lives there. It could be just a visit or trip.

What is the infinitive of mieszka and what aspect is it?

The infinitive is mieszkać.

It is imperfective, meaning it describes:

ongoing, habitual, or repeated actions
states without focusing on beginning or end

Mieszkać is used for “to live (somewhere)” as a state:

Mieszkam w Krakowie. – I live in Kraków.

The perfective counterpart is zamieszkać (“to start living somewhere / to move in”):

Mój wnuk zamieszkał za granicą. – My grandson moved abroad / started living abroad.

Where can I put teraz in the sentence, and does the word order change the meaning?

Common, natural positions:

Mój wnuk mieszka teraz za granicą.
Mój wnuk teraz mieszka za granicą.
Teraz mój wnuk mieszka za granicą.
Mój wnuk mieszka za granicą teraz. (possible but usually less neutral, often adds some emphasis)

The basic meaning stays the same: the situation is true now.

Subtle differences in emphasis:

Mój wnuk mieszka teraz za granicą.
Neutral; focuses on the verb “lives now”.
Mój wnuk teraz mieszka za granicą.
Slight emphasis on now, contrasting with a previous situation (e.g. he used to live here).
Teraz mój wnuk mieszka za granicą.
Stronger contrast with the past / another time frame: “Now, my grandson lives abroad (whereas before, something else was the case).”

In everyday speech, the first two are the most common and neutral.

What does za granicą literally mean, and why is granicą in that form?

Literally:

za = behind / beyond
granica = border, boundary
za granicą ≈ “beyond the border” → idiomatically “abroad”

Grammar:

The preposition za, when it means a location (“behind / beyond X”), uses the instrumental case.
Granica (nominative singular, feminine) in the instrumental singular is granicą.

So:

za + granicą → za granicą (“abroad,” as a location where someone is)

If you talk about movement to abroad, you use za + accusative:

jechać za granicę – to go abroad
- granica (nom.) → granicę (accusative singular)

So:

Mieszka za granicą. – He lives abroad. (location, instrumental)
Wyjechał za granicę. – He went abroad. (motion towards, accusative)

Is there a difference between za granicą and a single word zagranicą?

Yes, and it often confuses learners.

za granicą (two words)
- Preposition + noun in instrumental
- Very common, standard way to say “abroad” when it’s about location:
  - Mój wnuk mieszka za granicą.
zagranicą (one word)
- Historically, this can function as an adverb meaning “abroad,” but its use is limited and more formal / lexicalized (e.g. in some fixed phrases).
- In modern everyday language, za granicą is overwhelmingly preferred when talking about living/being abroad.

For speaking and most writing, using za granicą is safest and most natural.

Why is it teraz and not something like obecnie? Are they interchangeable?

Both exist, but they differ slightly in style and nuance:

teraz – “now”
- Very common, neutral, everyday speech.
- Refers to the present moment or current period.
obecnie – “currently / at present”
- A bit more formal or written.
- Often used in more official, informative contexts.

In your sentence:

Mój wnuk mieszka teraz za granicą. – perfectly natural, neutral.
Mój wnuk mieszka obecnie za granicą. – also correct, sounds slightly more formal or report-like.

Meaning is practically the same; you can usually swap them without changing much.

If I want to talk about a granddaughter instead, how does the sentence change?

For a granddaughter, you use wnuczka (feminine), so the possessive pronoun must agree in gender:

Mój wnuk mieszka teraz za granicą. – My grandson lives abroad now.
Moja wnuczka mieszka teraz za granicą. – My granddaughter lives abroad now.

Changes:

wnuk → wnuczka (masculine → feminine noun)
mój → moja (masculine possessor form → feminine possessor form)

The rest of the sentence stays the same.

Can I omit mój and just say Wnuk mieszka teraz za granicą?

You can say it, but it changes how it sounds:

Mój wnuk mieszka teraz za granicą.
Clearly “my grandson”.
Wnuk mieszka teraz za granicą.
Grammatically correct, but without context it sounds like:
- “The grandson lives abroad now” or
- You assume the listener already knows which grandson you mean (e.g. in a close family conversation where it’s obvious).

In Polish, possessive pronouns are sometimes omitted when the owner is obvious from context, but for clarity—especially in learner language—keeping mój is a good idea.

How is ó pronounced in mój and wnuk? Is it different from u?

Pronunciation:

ó is pronounced the same as u in modern standard Polish.
- mój → /muj/
- wnuk → /vnuk/

So phonetically:

ó = u

The difference is spelling, not sound. Historically they were different sounds, and spelling often reflects etymology or related word forms, for example:

mój but moi, moje (the stem vowel changes in some forms)
stół (table) but stoły (tables)

For speaking, you just pronounce both ó and u like English “oo” in “boot” (but shorter, without diphthong).

Why is it granicą with -ą at the end? What case is that?

Granicą is the instrumental singular of granica (“border”).

For most feminine nouns ending in -a, the instrumental singular is formed by changing -a → -ą:

kawa → kawą (coffee – with coffee)
siostra → siostrą (sister – with (my) sister)
granica → granicą (border – beyond/behind the border)

The preposition za, when it expresses location, requires the instrumental:

za granicą – beyond the border → abroad (where?)
za drzwiami – behind the door(s)
za domem – behind the house

So the -ą marks the instrumental case here.

Does the Polish present tense in mieszka correspond to English “lives” or “is living”?

In Polish, the simple present tense covers both English:

“lives” (simple present)
“is living” (present continuous)

Mój wnuk mieszka teraz za granicą. can be understood as:

“My grandson lives abroad now.”
“My grandson is living abroad now.”

Context decides whether it’s:

A more permanent situation (he has moved there)
A more temporary situation (he’s currently living there for some time)

Polish does not normally use a separate continuous tense for this. The simple present is enough.

Can I replace mieszka with żyje here?

No, not in this context.

mieszkać = to live (reside) somewhere
żyć = to live (be alive / have life / live one’s life)

So:

Mój wnuk mieszka teraz za granicą. – My grandson resides abroad now.
Mój wnuk żyje. – My grandson is alive.

You could say something like:

Mój wnuk żyje teraz za granicą.

This is grammatically correct, but it has a different feel:

It sounds like you’re commenting on the way he lives his life abroad (his lifestyle, situation), not just stating his address.

For neutral “he lives (resides) abroad,” mieszka is the correct and natural verb.