Si la funció acaba aviat, tornarem a casa en autobús.

In Catalan, a real/possible condition after si usually takes the present indicative, not the future.

So:

• Si la funció acaba aviat... = If the show ends early...

Even though the whole situation refers to the future, Catalan normally says:

• si + present
• then future in the main clause

That is exactly what happens here:

• Si la funció acaba aviat = if the show ends early
• tornarem a casa = we will go back home

This is similar to English, which also says If it rains, we’ll stay home, not If it will rain...

Here, la funció most naturally means the performance, the show, or the screening/session, depending on context.

Although funció can also mean function in other contexts, in everyday Catalan it is often used for things like:

• a theatre performance
• a cinema showing
• a staged event

So in this sentence, it probably means something like the show.

Because funció is a feminine noun in Catalan.

So it takes feminine forms:

• la funció
• una funció
• aquesta funció

This gender has to be learned with the noun. There is no special rule here that would let you predict it easily from English.

Acaba is the 3rd person singular present indicative of acabar (to finish / to end).

Conjugation:

• jo acabo
• tu acabes
• ell/ella acaba
• nosaltres acabem
• vosaltres acabeu
• ells/elles acaben

In the sentence, the subject is la funció (the show), which is third person singular, so:

• la funció acaba = the show ends

Yes, aviat often means soon, but in context it can also mean early or earlier than expected.

So:

• arribar aviat can mean to arrive early
• vine aviat can mean come soon

In this sentence:

• Si la funció acaba aviat...

the meaning is clearly If the show ends early.

So aviat is flexible, and context tells you whether it is closer to soon or early.

Tornarem is the 1st person plural future of tornar.

Here it means:

• we will return
• we will go back

So:

• tornarem a casa = we’ll go back home / we’ll return home

Conjugation of the future of tornar:

• jo tornaré
• tu tornaràs
• ell/ella tornarà
• nosaltres tornarem
• vosaltres tornareu
• ells/elles tornaran

Because a casa is an idiomatic expression meaning home / to home / at home, depending on context.

Examples:

• Som a casa = We are at home
• Vaig a casa = I’m going home
• Tornarem a casa = We’ll go back home

If you said a la casa, that would usually mean to the house as a physical building, not home in the general sense.

So:

• a casa = home
• a la casa = to the house

In Catalan, means of transport are very often introduced with en.

So:

• en autobús = by bus
• en tren = by train
• en cotxe = by car
• en avió = by plane

Using amb would usually sound like with a bus, which is not the normal way to express transport.

So for transportation, en is the usual choice.

After en for means of transport, Catalan often uses the noun without an article:

• en autobús
• en tren
• en metro

This works like English by bus, by train, where there is also no article.

So:

• en autobús = by bus

That is the standard expression.

When the si-clause comes first, a comma is normally used:

• Si la funció acaba aviat, tornarem a casa en autobús.

This helps separate the condition from the main clause.

If you reverse the order, the comma is often omitted:

• Tornarem a casa en autobús si la funció acaba aviat.

So the comma here is natural and standard.

Yes. Catalan allows both orders:

• Si la funció acaba aviat, tornarem a casa en autobús.
• Tornarem a casa en autobús si la funció acaba aviat.

Both mean the same thing.

The version with si first often sounds a bit more like you are setting up the condition first. The second version starts with the main action and adds the condition afterward.

The written accents show the stressed syllable:

• funció → stress on the last syllable: fun-ci-Ó
• autobús → stress on the last syllable: au-to-BÚS

That is one reason the accent marks are important in Catalan: they often tell you where the stress goes.

Also, the final -ó in funció is a clear stressed vowel, not reduced.

Yes, sometimes tornar can be translated as:

• return
• go back
• come back

The best English choice depends on perspective.

In this sentence, since the destination is a casa (home), English usually sounds most natural with:

• we’ll go back home
• we’ll return home

We’ll come back home is possible, but a bit less natural in many contexts.

It is completely normal, natural everyday Catalan.

Nothing in it is especially literary or formal. It is a very standard structure:

• Si + present
• future main clause
• common expressions like a casa and en autobús

So this is a very useful model sentence to learn.