Se o colchão não couber, vamos tirar a cadeira para abrir espaço no quarto.

Because couber is the future subjunctive form of caber.

In Portuguese, after se when you are talking about a possible future situation, Brazilian Portuguese usually uses the future subjunctive:

• Se o colchão não couber... = if the mattress doesn’t fit...
• Se ele vier... = if he comes...
• Se chover... = if it rains...

So:

• caber = infinitive, to fit
• cabe = present, it fits
• couber = future subjunctive, used here after se

This is one of the most important patterns to learn, because English does not have a separate form like this.

Yes. Caber is irregular, and that is why the form couber may look surprising.

Some useful forms are:

• caber = to fit
• cabe = it fits
• coube = it fit / it fitted
• cabia = it used to fit / would fit
• caberá = it will fit
• couber = if it fits / when it fits in a future sense

So couber is not built in a simple regular way from the infinitive. It is a form you basically need to recognize and memorize.

Here, caber means to fit physically into a space.

So the idea is that the mattress may be too big for the room or for the available space.

This verb is very common for space and size:

• A mesa não cabe na cozinha. = The table doesn’t fit in the kitchen.
• Tudo cabe na mala. = Everything fits in the suitcase.

It is not the same as English fit in the sense of clothing looking good on someone, or fit in socially. In this sentence, it is specifically about physical space.

Both are possible, but vamos tirar is usually more natural in everyday Brazilian Portuguese.

• vamos tirar = we’re going to remove / we’ll remove
• tiraremos = we will remove

In spoken Brazilian Portuguese, ir + infinitive is extremely common for future actions, often more common than the simple future.

So:

• Se o colchão não couber, vamos tirar a cadeira... sounds very natural and conversational.
• Se o colchão não couber, tiraremos a cadeira... is also correct, but a bit more formal or written.

No. Tirar here means to remove, take away, or move out of the way.

It does not automatically mean throwing it out permanently. In this context, it most likely means moving the chair so there is more room.

Depending on context, tirar can mean:

• remove
• take out
• take away
• move aside

So tirar a cadeira here is best understood as removing the chair from that spot to create space.

Because in Portuguese, para + infinitive is a very common way to express purpose, like to or in order to in English.

So:

• para abrir espaço = to make room / in order to open up space

This structure is extremely common:

• Estudo para aprender. = I study to learn.
• Fechei a porta para evitar barulho. = I closed the door to avoid noise.

Here, abrir espaço is an idiomatic expression meaning to make room or free up space.

Literally, abrir espaço is to open space.

But the natural English meaning is usually:

• make room
• free up space
• create space

In this sentence, it means making more physical room in the bedroom so the mattress can fit.

This is a very normal expression in Portuguese. It can be used literally or more figuratively depending on context.

Because no is the contraction of em + o.

So:

• em + o = no
• em + a = na
• em + os = nos
• em + as = nas

Therefore:

• no quarto = in the bedroom

This kind of contraction is mandatory in normal Portuguese. You generally do not say em o quarto.

In Portuguese, não normally comes before the verb it negates.

So:

• não couber = does not fit
• não cabe = does not fit
• não vamos tirar = we are not going to remove

That is the standard placement for negation in simple clauses.

So Se o colchão não couber... is the normal word order.

Because Portuguese nouns have grammatical gender.

• colchão is masculine, so it takes o
• cadeira is feminine, so it takes a

This does not necessarily mean the object is biologically male or female. It is just part of the grammar of the noun.

So you need to learn nouns together with their articles:

• o colchão
• a cadeira
• o quarto

This helps you remember gender more naturally.

In Brazilian Portuguese, colchão is approximately pronounced like kol-SHYOWN, but with an important nasal sound at the end.

A few pronunciation points:

• lh in Brazilian Portuguese is like a soft ly sound
• ão is a nasal ending, very common in Portuguese
• the stress is on the last syllable: col-CHÃO

So the hardest part for many English speakers is the nasal ão. You do not pronounce it like a clear English ow. The sound comes out through the nose as well.

Also, colchão means mattress, and its plural is colchões.

Yes, very common.

The pattern is:

• Se + future subjunctive, main clause

In this sentence:

• Se o colchão não couber = If the mattress doesn’t fit
• vamos tirar a cadeira para abrir espaço no quarto = we’ll remove the chair to make room in the bedroom

This is a very natural everyday structure for talking about possible future situations and what you will do in response.

You will hear the same pattern in sentences like:

• Se der tempo, eu vou. = If there’s time, I’ll go.
• Se você puder, me liga. = If you can, call me.
• Se chover, vamos ficar em casa. = If it rains, we’ll stay home.