Learn Hardcore Portuguese (Portugal): O carro não pode ir para trás aqui.

ir para trás = to go backwards / to reverse
ir atrás (normally ir atrás de…) = to go after / to chase
- e.g. ir atrás dele = to go after him / to chase him

If you said O carro não pode ir atrás aqui, it would sound like The car can’t go after (something/someone) here, which is wrong for the intended meaning.

For movement backwards, you need para trás (or another expression like recuar, dar marcha atrás).

Can I drop para and just say O carro não pode ir trás aqui?

No. Trás almost always needs a preposition in front of it:

para trás – backwards
por trás – behind (with the idea of by the back / from behind)

Trás alone is not normally used in modern Portuguese.
So ir trás is incorrect; you must say ir para trás.

Could I say O carro não pode recuar aqui or O carro não pode dar marcha atrás aqui instead?

Yes, both are natural and common in European Portuguese:

O carro não pode recuar aqui.
– The car can’t reverse here.
O carro não pode dar marcha atrás aqui.
– Literally The car can’t give reverse gear here, i.e. The car can’t reverse here.

Differences in feel:

ir para trás – very clear, everyday, neutral.
recuar – a bit more concise/neutral, also used figuratively (to retreat).
dar marcha atrás – very idiomatic in driving contexts, sounds very natural when talking about cars.

All three are fine in Portugal; context and style decide which you prefer.

Is não pode here more like “not allowed to” or “not able to”?

Poder can mean both to be allowed to and to be able to. The meaning depends on context:

In signs, instructions, or rules, não pode usually means “is not allowed to / must not”.
In physical or practical situations, it can also mean “cannot / is not able to”.

For this sentence:

Near a traffic sign or rule: “The car is not allowed to go backwards here.”
Describing a tight space or slope: “The car can’t go backwards here (it’s impossible or dangerous).”

The Portuguese phrase itself is ambiguous in the same way as English “can’t”; context clarifies it.

Why is the article O used before carro? Could I say just Carro não pode ir para trás aqui?

In European Portuguese, you normally need an article before singular countable nouns, even when English doesn’t:

O carro = the car
Um carro = a car

So:

O carro não pode ir para trás aqui. – The (specific) car can’t reverse here.
Um carro não pode ir para trás aqui. – A/any car can’t reverse here.

Bare Carro não pode… is ungrammatical in standard European Portuguese. Portuguese uses articles much more than English; dropping them works only in limited cases (titles, headlines, labels, some fixed expressions).

Why is não placed before pode and not somewhere else?

The normal position of não in Portuguese is immediately before the conjugated verb:

O carro não pode ir para trás aqui.
- pode is the conjugated verb (3rd person singular of poder)
- ir is an infinitive that depends on pode

So the pattern is:

[subject] + não + [conjugated verb] + [infinitive / rest of sentence]

Other examples:

Eu não quero sair. – I don’t want to go out.
Eles não podem entrar. – They can’t come in.

Putting não anywhere else (e.g. O carro pode não ir… or O carro não ir pode…) changes the meaning or is wrong.

Can I move aqui to another position, like Aqui o carro não pode ir para trás?

Yes. Aqui is a fairly flexible adverb, and all of these are grammatically correct:

O carro não pode ir para trás aqui.
O carro aqui não pode ir para trás.
Aqui o carro não pode ir para trás.

Differences:

O carro não pode ir para trás aqui. – The most neutral; aqui just states where.
O carro aqui não pode ir para trás. – Slight focus on “this car here / the car in this spot”.
Aqui o carro não pode ir para trás. – Emphasises the place: “Here, the car can’t go backwards.” (as opposed to other places).

In speech, word order is often used to highlight what’s important (place, subject, action).

How is pode ir pronounced in European Portuguese? Does it sound like one word?

In natural European Portuguese speech, pode ir is usually linked:

pode – /ˈpɔ.dɨ/ (roughly POH-dih)
ir – /iɾ/ (short eer with a tap r)

Spoken together, you’ll often hear something like:

pode ir → POH-dih-ir with the e of pode very reduced, almost [ɨ] or barely audible.

Also note:

não – nasal vowel, like now but more nasal and closed: /nɐ̃w̃/ or /nɐ̃ũ/.
carro – initial r is a strong throaty sound in European Portuguese: /ˈka.ʁu/.
para – often reduced in connected speech to something like /prɐ/ (though still written para in careful writing).

So a fluent European speaker might say something close to:

[o ˈka.ʁu nɐ̃w̃ ˈpɔ.dɨ iɾ pɾɐ ˈtɾaʃ aˈki]

What’s the difference between atrás, detrás, and por trás?

They’re all related to the idea of “behind”, but used differently:

atrás – behind, at the back (more general)
- O carro está atrás da casa. – The car is behind the house.
detrás de – from behind / at the back of (feels a bit more formal/literary)
- Saiu de detrás da porta. – He came out from behind the door.
por trás de – behind, from the back side (often with the idea of by way of the back or not from the front)
- Entrou por trás da casa. – He went in round the back of the house.

For movement backwards, you don’t use these alone; you use:

para trás – backwards
- ir para trás, andar para trás, dar um passo para trás

What’s the difference between aqui and cá? Could I say O carro não pode ir para trás cá?

Cá and aqui both mean here, but they’re not interchangeable everywhere.

aqui – neutral, works in almost all situations: place and direction.
cá – more colloquial and has restrictions in use:
- very common in expressions like vir cá, estar cá, chegar cá (movement/being “here” relative to the speaker)
- not normally used after a verb of movement with a clear direction like ir para trás in this sentence.

So:

O carro não pode ir para trás aqui. ✅ natural, correct.
O carro não pode ir para trás cá. ❌ sounds wrong/unnatural.

But:

Vem cá. / Vem aqui. – Both accepted (though vem cá is very common).
Fica cá comigo. – Stay here with me.

How is pode conjugated, and why is it pode here and not something else?

Poder (to be able to / to be allowed to) in the present tense (indicative):

eu posso – I can
tu podes – you can (informal singular)
ele / ela / você pode – he/she/you (formal) can
nós podemos – we can
vocês podem – you (plural) can
eles / elas podem – they can

In the sentence O carro não pode ir para trás aqui:

The subject is o carro = it (3rd person singular).
So we use pode (3rd person singular), just like ele pode.

If the subject changed, the verb would change:

Os carros não podem ir para trás aqui. – The cars can’t go backwards here.
Eu não posso ir para trás aqui. – I can’t go backwards here.