Learn Hardcore Esperanto: Mia amiko invitas nin al festo, kie ni dancos kaj aŭskultos laŭtan muzikon. - My friend invites us to a party where we will dance and listen to loud music.

Possessive + noun usually doesn’t take “la”
- Mia amiko literally means my friend.
- In Esperanto, when you use a possessive adjective (mia, via, lia, ŝia, nia, ilia, etc.), you normally do not also add la.
- So you say:
  - Mia amiko = my friend
  - Via domo = your house
- You could say la mia amiko, but that sounds unnatural in this context; la mia is usually used alone and means mine:
  - Tiu estas la mia. = That one is mine.
No indefinite article, and “la” only for the
Esperanto has only one article: la = the.
There is no word for a / an.
- festo alone = a party
- la festo = the party (a specific, known party)

In the sentence:

al festo = to a party (not yet identified as a specific, known one)

If you wanted to the party, you would say:

al la festo = to the party

Why is it al festo and not al feston?

Because after a preposition like al, you normally do not add the accusative -n, unless you are using a special “direction” use with a preposition that does not itself express direction.

al already means to, towards, so it already shows direction.
Therefore:
- al festo = to a party
- al la festo = to the party
  and not al feston.

Compare:

Mi vidas la feston. = I see the party.
- Here, feston is a direct object, so it gets -n.
Mi iras al la festo. = I go to the party.
- Here, the direct object is missing (there is none), and la festo is just the object of al, so no -n.

The accusative -n is for:

direct objects (Mi amas vin.),
and some special uses like direction without a preposition (Mi iras Londonon. = I go to London).

But not after al, because al already means “to”.

What exactly does kie mean here, and why not kiam or ke?

Here kie is a relative adverb meaning where / at which place and refers back to festo:

…al festo, kie ni dancos kaj aŭskultos…
= …to a party, where we will dance and listen…

So kie = where / in which place, pointing to the location of the party.

Why not the others?

kiam = when / at what time
- You would use kiam if the preceding word referred to time, not to a place:
  - Je la horo, kiam ni dancos… = At the time when we will dance…
- But festo is an event/place here, not a time expression, so kie fits better.
ke = that (introduces a content clause)
- ke does not refer back to a noun; it just introduces something reported or stated:
  - Li diris, ke ni dancos. = He said that we will dance.
- In al festo, ke ni dancos…, ke would be ungrammatical.

You could rewrite using en kiu:

al festo, en kiu ni dancos… = to a party, in which we will dance…

…but kie is shorter and completely natural.

Why is there a comma before kie?

The comma marks the beginning of a relative clause that gives extra information about festo.

Mia amiko invitas nin al festo, kie ni dancos kaj aŭskultos laŭtan muzikon.

This is like English:

…to a party, where we will dance and listen to loud music.

In Esperanto, using a comma before a relative clause (introduced by kiu, kie, kiam, etc.) is very common and helps readability.

There is also a subtle nuance similar to English:

With comma: al festo, kie… → “to a party, where…”
- Describes the party, but doesn’t really choose it from among others; it’s just extra info.
Without comma: al festo kie…
- More like “to that party where…” (restrictive), choosing one particular party from among several possible ones.

In practice, especially in simple sentences, many writers always use the comma here, and that is perfectly acceptable.

Why are dancos and aŭskultos future (-os), but invitas is present (-as)?

Because they describe actions happening at different times:

invitas (-as) = present tense
→ The invitation is happening now (or is valid now).
dancos, aŭskultos (-os) = future tense
→ The dancing and listening will happen later, at the party.

So the overall meaning is:

Mia amiko invitas nin… = My friend is inviting us…
…kie ni dancos kaj aŭskultos… = …where we will dance and listen…

You could also change invitas to another tense depending on the context:

Mia amiko invitis nin al festo, kie ni dancos…
= My friend invited us to a party where we will dance…
- The invitation is already in the past, but the party is still in the future.

Esperanto tenses are:

-as = present
-is = past
-os = future
-us = conditional
-u = imperative / jussive

Each verb is marked relative to now, not relative to the other verbs.

Why do both laŭtan and muzikon end with -n?

Because the whole phrase laŭta muziko is the direct object of aŭskultos, and in Esperanto:

All nouns in the direct object take -n.
All adjectives describing that noun agree with it in case and number.

Base forms:

laŭta muziko = loud music

As direct object:

Ni aŭskultos laŭtan muzikon. = We will listen to loud music.

Both words change:

muziko → muzikon (noun gets -n)
laŭta → laŭtan (adjective agrees with the noun)

More examples:

Mi vidas grandan hundon. = I see a big dog.
Mi vidas grandajn hundojn. = I see big dogs.
grandaj hundoj (subject)
grandajn hundojn (direct object)

So: if the noun takes -n as direct object, any adjective attached to it also takes -n.

Could I say aŭskultos laŭte muzikon instead of aŭskultos laŭtan muzikon? What’s the difference?

You can say aŭskultos laŭte muzikon, but the meaning is slightly different:

laŭta = loud (adjective, describes a thing)
- laŭta muziko = loud music (the music is loud)
laŭte = loudly (adverb, describes how you do something)
- aŭskulti laŭte = to listen loudly (you are loud while listening)

In your sentence:

aŭskultos laŭtan muzikon = we will listen to loud music
→ The music itself is loud (this matches English “listen to loud music”).

If you said:

aŭskultos laŭte muzikon
→ we will listen to music loudly (we will be loud / the manner of listening is loud)

Both are grammatically correct, but:

To say loud music, use laŭta muziko / laŭtan muzikon.
To say listen loudly, use aŭskulti laŭte.

I thought every noun as an object gets -n, so why doesn’t festo have -n here?

The key is to distinguish:

Direct objects of verbs → take -n
Objects of prepositions → normally do NOT take -n

In the sentence:

nin is the direct object of invitas → nin (with -n)
al festo is just a prepositional phrase (to a party) → festo, no -n

Compare:

Mi vidas la feston. = I see the party.
- la feston = direct object → gets -n.
Mi iras al la festo. = I go to the party.
- al la festo is introduced by al, so the noun does not get -n.

The accusative -n with prepositions is used mainly for added direction when the preposition itself doesn’t show direction, e.g.:

sur la tablo = on the table (location)
sur la tablon = onto the table (movement to)

But al already is a directional preposition (“to”), so you don’t add -n:

✅ al festo
❌ al feston (wrong / redundant)

Could I change the word order, like Mia amiko nin invitas al festo? How free is the word order here?

Esperanto word order is fairly flexible, because the accusative -n shows grammatical roles. However, there are still natural and less natural orders.

Your original:

Mia amiko invitas nin al festo, kie ni dancos kaj aŭskultos laŭtan muzikon.
(Subject–Verb–Object is the neutral, most natural order.)

Other possible orders (still correct):

Mia amiko nin invitas al festo…
→ Slight emphasis on nin (“My friend is inviting us to a party”).
Nin invitas mia amiko al festo…
→ Strong emphasis on nin (maybe contrasting us with someone else).
Al festo mia amiko invitas nin…
→ Emphasis on al festo (“To a party my friend is inviting us”).

Inside the kie-clause you also have some flexibility:

kie ni aŭskultos laŭtan muzikon kaj dancos
kie ni dancos kaj aŭskultos laŭtan muzikon

Both are fine; you just choose the order you prefer or want to emphasize.

Basic guidelines:

For clear, natural Esperanto, especially as a learner, prefer Subject–Verb–Object.
Keep prepositions with their nouns (al festo, not separated).
Move phrases mainly for emphasis or style, not randomly.

Why is it aŭskultos laŭtan muzikon and not aŭskultos al laŭta muziko, like “listen to loud music” in English?

In Esperanto, aŭskulti already includes the idea of “to”:

aŭskulti ion = to listen to something
It takes a direct object, not a prepositional phrase.

So:

✅ aŭskulti muzikon = to listen to music
✅ aŭskulti laŭtan muzikon = to listen to loud music
❌ aŭskulti al muziko (this is not standard Esperanto)

Some similar pairs:

aŭskulti radion = listen to the radio
aŭskulti la instruiston = listen to the teacher

By contrast, some verbs do require al:

helpi al iu = to help someone
paroli al iu = to speak to someone

So in your sentence, aŭskultos laŭtan muzikon is exactly the right pattern:
aŭskulti + direct object (with accusative -n).

Is festo the normal word for “party”? Does it mean “feast” or “festival” too?

Yes, festo is the standard, general word for party / celebration / feast / festival, depending on context.

Common uses:

naskiĝtaga festo = birthday party
novaĵjara festo = New Year’s party
religia festo = religious festival / feast
ŝtata festo = public holiday (national celebration day)

If you need to be very specific, there are other words:

festeno = banquet, formal feast (more about the meal itself)
kunveno = meeting / gathering (not necessarily festive)
bal(o) = ball (formal dance party)
diskoteko = disco / club

But in everyday speech, festo is the normal, broad word for party or celebration, so in your sentence it’s exactly right.