A la mare li agrada la música.

Because agradar does not work like English to like.

In Catalan, agradar is more like to be pleasing to. So the structure is:

• la música = the thing that is pleasing
• a la mare / li = the person it is pleasing to

So literally, the sentence is closer to:

• Music is pleasing to mother

That is why la mare is not the subject here in the usual English sense.

The grammatical subject is la música.

You can tell because the verb agrada agrees with la música, which is singular.

• la música → singular → agrada
• if it were plural, you would get agraden

For example:

• A la mare li agrada la música. = Mother likes music.
• A la mare li agraden els concerts. = Mother likes concerts.

So even though the mother is the person who likes something, la música is the grammatical subject.

Yes, they both point to the same person, and this is very normal in Catalan.

This is called clitic doubling. In sentences with agradar, Catalan usually uses:

• the full phrase: a la mare
• plus the indirect object pronoun: li

So:

• A la mare li agrada la música

is the natural standard pattern.

The li is not optional in normal usage when the person is expressed like this. It helps mark clearly who experiences the liking.

Li is the indirect object pronoun meaning to him / to her / to you (formal singular).

In this sentence, it refers to la mare.

So:

• A la mare = to the mother
• li = to her

Together they mean:

• To the mother, music is pleasing
• in natural English: The mother likes music

The a introduces the indirect object: the person to whom something is pleasing.

With agradar, the person who likes something is normally introduced by a:

• A la mare li agrada la música.
• Al nen li agrada jugar.
• A mi m’agrada el cafè.

So a here means something like to.

Because la música is singular.

The verb agradar agrees with the thing being liked, not with the person who likes it.

• la música = singular → agrada
• les cançons = plural → agraden

Compare:

• A la mare li agrada la música.
• A la mare li agraden les cançons catalanes.

This is one of the most important things to remember with agradar.

Catalan often uses the definite article with general or abstract nouns where English does not.

So:

• la música = music, in a general sense
• el cafè = coffee
• el futbol = football/soccer

This is completely normal in Catalan. You should not try to match English article use too closely.

It can often mean my mother depending on context.

In Catalan, especially in everyday speech, family members are often referred to with the definite article:

• la mare = my mother / mother
• el pare = my father / father

So A la mare li agrada la música will often be understood as:

• My mother likes music

But in another context it could also mean the mother. Context tells you which meaning is intended.

Yes. Catalan allows some flexibility in word order.

These are possible:

• A la mare li agrada la música.
• La música li agrada a la mare.
• Li agrada la música a la mare.

They all mean roughly the same thing, but the focus changes a little.

The version you were given is a very common, clear order, especially if you want to highlight who likes the music.

Yes, if it is already clear who li refers to.

• Li agrada la música. = He/She likes music.

But without context, li is ambiguous: it could mean to him, to her, or to you (formal singular).

That is why adding a la mare makes the sentence specific and clear.

It can be used with both nouns and actions.

With a noun:

• A la mare li agrada la música. = Mother likes music.

With an infinitive:

• A la mare li agrada cantar. = Mother likes singing / likes to sing.

In both cases, the same basic pattern stays the same: someone + indirect object + agradar + thing/activity that is pleasing.

You put no before the pronoun and verb:

• A la mare no li agrada la música. = Mother does not like music.

The order is normally:

• A la mare
  • no
    • li agrada
      • la música

So the pronoun stays there even in the negative.

You can simply use intonation in speech, or question marks in writing:

• A la mare li agrada la música? = Does mother like music?

You could also ask with a question word:

• A la mare li agrada la música o el teatre? = Does mother like music or theatre?
• Què li agrada a la mare? = What does mother like?

Notice that li still stays in the sentence.