Learn Hardcore Spanish (Spain): Mi hermano se queda quieto cuando escucha esa música. - My brother stays still when he listens to that music.

Mi hermano se queda quieto ≈ “My brother stays/keeps still” or “He ends up still.”
Without se, quedar is less commonly used in this sense for people in everyday speech.
Mi hermano queda quieto is grammatically possible, but it sounds much less natural; the idiomatic expression is quedarse quieto.

So se is needed because quedarse quieto is the standard, set phrase for “to keep still” in Spanish.

What’s the general difference between quedar and quedarse?

They’re related but not interchangeable.

Quedar (non‑reflexive) often means:

to remain / to be left (over):
- Me quedan dos euros. – “I have two euros left.”
to arrange to meet:
- Quedamos mañana a las seis. – “Let’s meet tomorrow at six.” / “We’re meeting tomorrow at six.”
to suit / to fit (clothing):
- Ese vestido te queda bien. – “That dress suits you / fits you well.”

Quedarse (reflexive) focuses on the subject staying somewhere or ending up in some state:

to stay (in a place):
- Me quedo en casa. – “I’m staying at home.”
to end up / become and remain in a state:
- Se quedó dormido. – “He fell asleep (and stayed asleep).”
- Se queda quieto. – “He keeps / stays still.”

In your sentence, we’re talking about your brother ending up and staying still when he hears that music, so quedarse is the right form.

Why is it quieto and not quieta, quietos, etc.?

In Spanish, adjectives agree in gender and number with the noun they describe.

The subject is mi hermano:
- hermano = masculine, singular
Therefore the adjective must also be masculine, singular:
- quieto

Other possibilities:

Mi hermana se queda quieta. – feminine singular
Mis hermanos se quedan quietos. – masculine plural or mixed group
Mis hermanas se quedan quietas. – feminine plural

Why do we use escucha instead of oye? What’s the difference between escuchar and oír?

Basic difference:

oír = to hear (perceive sound, more passive)
escuchar = to listen (to) (pay attention intentionally)

So:

Mi hermano se queda quieto cuando oye esa música.
= “My brother keeps still when he hears that music.” (he perceives it)
Mi hermano se queda quieto cuando escucha esa música.
= “My brother keeps still when he listens to that music.” (he’s actively listening)

In many real conversations, people sometimes use oír in places where English would say “listen,” but the textbook / neutral choice for “listens to that music” is escucha esa música, which is what you see here.

Why don’t we need a before esa música after escucha?

Because escuchar normally takes a direct object without a preposition.

Escuchar algo:
- Escucha la radio. – “He listens to the radio.”
- Escucho música. – “I listen to music.”
You only use a when the direct object is a person (the “personal a”) or something personified:
- Escucho a mi hermano. – “I listen to my brother.”
- Escucho al profesor. – “I listen to the teacher.”

In escucha esa música, esa música is just a normal direct object (not a person), so no “a” is needed.

Can we change the word order, like Cuando escucha esa música, mi hermano se queda quieto?

Yes. Both orders are correct:

Mi hermano se queda quieto cuando escucha esa música.
Cuando escucha esa música, mi hermano se queda quieto.

This cuando‑clause is an adverbial clause of time. In Spanish it can go:

at the end (no comma in the middle), or
at the beginning (normally followed by a comma).

The meaning doesn’t change; it’s just a stylistic choice.

Why is it cuando escucha esa música and not cuando escuche esa música or a future tense?

Cuando can take either indicative or subjunctive, depending on the meaning:

Indicative (here: escucha) for habitual / general actions or facts:
- Mi hermano se queda quieto cuando escucha esa música.
  = Whenever he hears/listens to that music, he keeps still.
  (This is something that generally happens.)
Subjunctive (escuche) with cuando for future, not-yet-real events:
- Cuando escuche esa música, se quedará quieto.
  = When he hears that music (in the future), he will keep still.
  (You’re talking about a specific future situation that hasn’t happened yet.)

So your sentence describes a regular pattern, not a one‑off future event. That’s why we use cuando escucha (present indicative), not cuando escuche.

What exactly does esa express in esa música? How is it different from esta música or aquella música?

Spanish has three main demonstratives:

esta / este – this (near the speaker)
esa / ese – that (near the listener, or not especially near either person; “that” in a neutral sense)
aquella / aquel – that… over there (far from both, or distant in time / context)

In practice:

esta música – this music (very “here and now”: maybe it’s playing right next to you)
esa música – that music (already known, mentioned, or not right “here”; often “that music [we’re talking about]”)
aquella música – that (distant) music (far away, or from a distant time in the past)

In your sentence, esa música suggests “that particular music” you both know about. Depending on tone, esa música can also sometimes sound a bit dismissive (“that music (of his)”).

When do we write cuando with an accent (cuándo)?

Use cuándo (with accent) only when it’s interrogative or exclamative:

Direct questions:
- ¿Cuándo vienes? – “When are you coming?”
Indirect questions:
- No sé cuándo vienes. – “I don’t know when you’re coming.”
Exclamations:
- ¡Cuándo aprenderás! – roughly “When will you ever learn!”

Use cuando (no accent) as a conjunction or relative word, like in your sentence:

Mi hermano se queda quieto cuando escucha esa música.
Cuando era niño, vivía en Madrid. – “When he was a child, he lived in Madrid.”

Could we also say Mi hermano está quieto cuando escucha esa música? What’s the difference from se queda quieto?

You can say it, but the nuance changes:

estar quieto = to be still (describes a state at a given moment)
- Mi hermano está quieto cuando escucha esa música.
  = “My brother is still when he listens to that music.”
  (Describes his condition during that time.)
quedarse quieto = to become and stay still (change + result)
- Mi hermano se queda quieto cuando escucha esa música.
  = “My brother keeps / stays still when he listens to that music.”
  (He stops moving and remains still; the music causes this behavior.)

So se queda quieto is more dynamic and cause‑and‑effect: the music makes him stop moving and stay that way. Está quieto just states how he is, without emphasizing the change.