Learn Hardcore Portuguese (Brazil): Se alguém ligar, diga que eu estou no cinema com minha irmã. - If someone calls, say that I am at the movie theater with my sister.

Se alguém ligar = If someone calls (at some future time)…
Se alguém liga would sound more like a general truth or habit: If someone calls (in general)… and doesn’t fit so well for a one‑time future situation.
Se alguém vai ligar is grammatically possible, but less natural here. Brazilians strongly prefer “se + future subjunctive” in this kind of sentence.

So “Se alguém ligar, …” is the standard way to say “If someone calls, …” about a future possibility.

What verb form is “ligar” here? It looks like the infinitive.

Here “ligar” is future subjunctive, not infinitive, even though it looks the same.

Infinitive: ligar = to call
Future subjunctive (eu/ele/você): ligar = when/if I/he/you call

You recognize it’s future subjunctive because:

It comes after “se” (if),
It refers to a future, uncertain event: if someone happens to call.

Examples with the same pattern:

Se ele chegar cedo, me avisa. – If he arrives early, let me know.
Quando ela ligar, eu falo com ela. – When she calls, I’ll talk to her.

In all of these, the form is identical to the infinitive, but the function is future subjunctive.

Why do we use “diga” and not “dizer” or “diz”?

Because “diga” is the imperative form for “você” (the usual “you” in Brazil).

Verb: dizer (to say / to tell)
Present subjunctive (eu/ele/você): diga
Affirmative imperative (você): diga

So “diga que eu estou no cinema” = “tell (someone) that I am at the movies.”

“dizer” is just the infinitive (to say), so you can’t use it as a command here.
“diz” is the informal command for “tu” in some regions, and also used colloquially with você in some places, but “diga” is the neutral, standard imperative across Brazil.

How would this sentence change in very informal speech with a friend?

A very typical informal version might be:

Se alguém ligar, fala que eu tô no cinema com a minha irmã.
- fala = informal imperative of falar (“say / tell”)
- tô = colloquial pronunciation/spelling of estou
- a minha irmã: adding the article is common in many regions informally

Or, keeping dizer:

Se alguém ligar, diz que eu tô no cinema com a minha irmã.

Both are very natural in casual conversation. The original “diga” feels a bit more polite / careful / neutral, good in most contexts.

Why is there a comma after “ligar”?

Portuguese uses a comma to separate the dependent clause from the main clause:

Dependent clause (condition): Se alguém ligar – If someone calls
Main clause (result/instruction): diga que eu estou no cinema… – tell them I’m at the movies…

So:

Se alguém ligar, diga que eu estou no cinema…

You could invert the order:

Diga que eu estou no cinema com minha irmã se alguém ligar.

In that case, a comma is optional and usually omitted:

Diga que eu estou no cinema com minha irmã se alguém ligar.

Do I have to say “eu” in “eu estou no cinema”, or can I just say “estou no cinema”?

You don’t have to say “eu”. Both are correct:

Eu estou no cinema.
Estou no cinema.

In Portuguese, subject pronouns (eu, você, ele, etc.) are often dropped because the verb ending usually shows who the subject is.

We keep “eu” when:

we want to emphasize the subject:
- Eu estou no cinema (not someone else).
we want extra clarity, or it just feels natural in the sentence’s rhythm.

In your sentence, “eu estou no cinema” and “estou no cinema” are both normal.

What exactly does “no” mean in “no cinema”?

“No” is a contraction in Portuguese:

em (in / at) + o (the, masculine singular) → no

So:

no cinema = em + o cinema = in the / at the movie theater

More examples:

no carro = in the car
no trabalho = at work
no Brasil = in Brazil

Why is it “minha irmã” and not “a minha irmã”? Are both correct?

In Brazilian Portuguese, both are possible:

minha irmã – my sister
a minha irmã – literally the my sister

Differences:

In Brazil, with close family members, it’s very common to omit the article:
- minha mãe, meu pai, minha irmã.
Using the article (a minha irmã) is also heard, and it’s very common in European Portuguese and in some Brazilian regions.

Here, “minha irmã” is completely natural and maybe slightly more neutral/standard in Brazil. You could also say:

Se alguém ligar, diga que eu estou no cinema com a minha irmã.

Both versions are correct in Brazilian Portuguese.

Does “alguém” behave as singular or plural? Could I ever use a plural verb like “ligarem” with it?

“Alguém” is grammatically singular.

Se alguém ligar – correct
Se alguém ligarem – incorrect

Even though someone in English could refer to more than one unknown person, Portuguese still treats alguém as singular for verbs and pronouns.

If you really want a plural idea, you’d use a different word:

Se algumas pessoas ligarem, diga… – If some people call, tell them…

Does “ligar” always mean “to call (on the phone)” in Brazilian Portuguese?

No, “ligar” is a very flexible verb. In your sentence, it does mean “to call (on the phone)”:

Se alguém ligar… – If someone calls (on the phone)…

But it can also mean:

to turn on (a device)
- Ligar a luz. – Turn on the light.
- Ligue a TV. – Turn on the TV.
to connect / to link
- Essa estrada liga as duas cidades. – This road connects the two cities.
to care (about something) – colloquial with “ligar para”
- Eu não ligo pra isso. – I don’t care about that.

So you know it means “call on the phone” here because of the common expression “ligar (para alguém)” in a context involving someone contacting you.

Why is it “no cinema” and not “no filme” if the meaning is “at the movies”?

In Brazilian Portuguese:

no cinema = at the movie theater / at the movies (the place)
no filme = in the movie (inside the film’s story or content)

So:

Estou no cinema. – I’m at the movie theater.
Ele aparece no filme. – He appears in the movie.

When English says “at the movies” to mean at the movie theater, Portuguese uses “no cinema”, not “no filme”.