Os dois vão ao teatro amanhã.

Os dois means the two or both of them.

In Portuguese, adding os makes the phrase specific: you are talking about two particular people already known in the context.

• os dois = the two / both
• dois by itself usually means just two

So:

• Os dois vão ao teatro amanhã. = The two of them are going to the theater tomorrow.
• Dois vão ao teatro amanhã. = Two are going to the theater tomorrow.
  This sounds less specific and more incomplete unless the context is very clear.

It can mean either, depending on context.

In this sentence, os dois is very naturally understood as both of them or the two.

Portuguese often uses os dois where English might prefer both:

• Os dois chegaram. = Both arrived.
• Vi os dois na rua. = I saw the two of them / both of them on the street.

A more formal alternative is ambos, but in everyday Brazilian Portuguese, os dois is much more common.

Because the subject is plural: os dois = the two of them.

The verb ir (to go) must agree with the subject:

• eu vou = I go / I’m going
• você/ele/ela vai = you/he/she goes / is going
• eles/elas vão = they go / are going

Since os dois refers to two people, Portuguese uses the third person plural form:

• Os dois vão...

If it were just one person, it would be:

• Ele vai ao teatro amanhã.

The tilde in vão marks nasal pronunciation and also distinguishes this form from other similar-looking words.

Vão is the they/you all form of ir in the present tense:

• eles vão = they go / they are going

The nasal sound is important in pronunciation. The word is roughly pronounced like vowng, with a nasal ending rather than a clear n sound.

So the tilde is not optional—it is part of the correct spelling and pronunciation.

Ao is a contraction of:

• a = to
• o = the

So:

• a + o = ao

Portuguese normally contracts these two words when they come together.

Examples:

• ao teatro = to the theater
• ao mercado = to the market
• ao médico = to the doctor

Other common contractions are:

• a + a = à
• a + os = aos
• a + as = às

Because teatro here is a masculine singular noun and it normally takes the definite article o when you mean the theater.

So:

• a + o teatro → ao teatro

In Portuguese, articles are often used more than in English. English sometimes says go to school, go to church, go to bed without the, but Portuguese often uses an article depending on the expression.

Here, ir ao teatro is the normal way to say to go to the theater.

It can mean either one.

In Portuguese, the present tense often covers both:

• a general present: they go
• a near-future or planned action: they are going

Because the sentence includes amanhã (tomorrow), the natural English translation is usually:

• The two are going to the theater tomorrow.
• or The two will go to the theater tomorrow.

Portuguese often uses the present tense to talk about scheduled or planned future events.

Because that is a very natural place for a time expression in Portuguese.

The basic structure here is:

• subject + verb + place + time
• Os dois + vão + ao teatro + amanhã

But Portuguese is flexible, and you could also say:

• Amanhã, os dois vão ao teatro.
• Os dois vão amanhã ao teatro.
  This is possible, though less natural in many everyday contexts.

Putting amanhã at the end sounds very normal and neutral.

Yes, you can.

Portuguese often allows the subject to be omitted when the verb form makes it clear who is being referred to. Since vão is plural, it already suggests they.

So:

• Vão ao teatro amanhã. = They’re going to the theater tomorrow.

However, keeping os dois adds emphasis or clarity:

• it tells you exactly that it is the two of them
• it can contrast them with other people

So the full sentence is more specific than just Vão ao teatro amanhã.

Yes, in most everyday Brazilian Portuguese, os dois is more natural.

Compare:

• Os dois vão ao teatro amanhã. = everyday, common
• Ambos vão ao teatro amanhã. = correct, but more formal or written

A learner should definitely understand ambos, but for normal conversation, os dois is often the better choice.

A rough pronunciation guide is:

ooz doys VOWng ow teh-AH-troo ah-mah-NYAH

A few important points:

• Os often sounds like ooz in Brazilian Portuguese.
• dois sounds roughly like doys.
• vão has a nasal sound.
• ao sounds like ow.
• teatro in Brazilian Portuguese is often pronounced close to teh-AH-tro or chee-AH-tro depending on accent and speed.
• amanhã ends with a nasal ã sound, and the stressed syllable is the last one: -nhã.

The stress in the sentence naturally falls on words like dois, vão, teatro, and amanhã.

Because of amanhã, it refers to a future event.

Without amanhã, Os dois vão ao teatro could mean:

• The two go to the theater
• The two are going to the theater

But once you add amanhã, it clearly points to tomorrow, so it is understood as a future plan or scheduled action.

That is a very common use of the present tense in Portuguese.