Per entrar al museu, cal comprar una entrada.

Per + infinitive is a very common way in Catalan to mean in order to + verb or simply to + verb when expressing purpose.

So:

• Per entrar al museu = To enter the museum / In order to enter the museum

This is similar to Spanish para + infinitive, but in Catalan per is often used in this kind of structure.

Examples:

• Per obrir la porta, cal una clau. = To open the door, a key is needed.
• Per aprendre català, cal practicar. = To learn Catalan, you need to practise.

Cal means it is necessary, one must, or you need to.

In this sentence:

• cal comprar una entrada = it is necessary to buy a ticket

It is an impersonal verb form, so it does not change depending on who is doing the action. It is used very often in Catalan.

Examples:

• Cal estudiar. = It is necessary to study.
• Cal arribar d’hora. = You need to arrive early.

A very natural English translation is often:

• you have to
• you need to
• it’s necessary to

Because al is the contraction of:

• a + el = al

So:

• al museu = to the museum

This contraction is required when a comes before the masculine singular article el.

Other common contractions:

• del = de + el
• pel = per + el

Examples:

• Vaig al cinema. = I’m going to the cinema.
• La porta del museu = The door of the museum.

Entrada can mean either:

• entry / entrance
• ticket

In this sentence, una entrada means a ticket.

So even though the sentence already has entrar (to enter), the noun entrada is not repeating the same idea awkwardly. It is simply the normal word for ticket in many Catalan contexts, especially for museums, cinemas, concerts, etc.

Examples:

• He comprat dues entrades. = I bought two tickets.
• On és l’entrada? = Where is the entrance?

Context tells you which meaning is intended.

Yes. In Catalan, entrar is often used directly, without adding a preposition before the place.

So:

• entrar al museu = enter the museum / go into the museum

This is more like English enter the museum than English go into the museum.

Catalan commonly says:

• entrar a casa = go into the house / enter the house
• entrar al cotxe = get into the car

So it is normal that the verb itself is just entrar, not something like entrar a dins de here.

Both order and emphasis matter.

The sentence begins with Per entrar al museu to set the situation first:

• As for entering the museum...
• To enter the museum...

Then it gives the requirement:

• cal comprar una entrada

This is a very natural structure in Catalan when you want to present a condition or purpose first.

You could also say:

• Cal comprar una entrada per entrar al museu.

That is also correct and natural. It just places the necessity first instead of the purpose first.

Sometimes yes, but not always directly.

Cal often corresponds to:

• it is necessary
• you need to
• you have to
• sometimes must

In this sentence:

• Per entrar al museu, cal comprar una entrada. could be translated as
• To enter the museum, you have to buy a ticket.

That is very natural English.

But grammatically, cal is not exactly the same as English must, because it is impersonal. It does not behave like a normal personal verb.

Yes.

It can be followed by:

1. an infinitive
   
   • Cal comprar una entrada.
2. a noun phrase introduced indirectly depending on structure
   
   • Cal una entrada. = A ticket is needed.

So in this context, both are possible:

• Cal comprar una entrada. = It’s necessary to buy a ticket.
• Cal una entrada. = A ticket is required.

The first stresses the action of buying; the second stresses the thing required.

Because entrada is a feminine singular countable noun.

So:

• una entrada = a ticket

Catalan articles:

• un = a/an for masculine singular nouns
• una = a/an for feminine singular nouns

Examples:

• un llibre = a book
• una porta = a door
• una entrada = a ticket

A couple of useful points:

• cal is short and simple, roughly like kahl
• entrada has the stress on -tra-: en-TRA-da
• museu is stressed on the last syllable: mu-se-EU

Also, in normal speech, al museu flows together quite smoothly.

If you are reading the whole sentence aloud, a natural rhythm is:

Per entrar al museu, cal comprar una entrada.

with a slight pause after museu.

Usually, in standard Catalan, entrar al museu is the more natural form here.

Why?

• al = a + el
• with places, entrar a / al / a la / als / a les is very common

So:

• entrar al museu is the standard and expected phrasing.

You may sometimes see other constructions in different contexts or varieties, but for a learner, entrar al museu is the safest and most natural choice.

A very useful pattern is:

Per + infinitive, cal + infinitive / noun

So you can build many sentences like this:

• Per viatjar a l’estranger, cal passaport. = To travel abroad, a passport is needed.
• Per fer aquest exercici, cal pensar una mica. = To do this exercise, you need to think a little.
• Per obrir el fitxer, cal una contrasenya. = To open the file, a password is required.

This pattern is very common and very useful in everyday Catalan.