Learn Hardcore Spanish (Latin America): Mi hermana dice que debería dormir más, pero siempre se acuesta tarde. - My sister says she should sleep more, but she always goes to bed late.

In Spanish, when a verb like decir (to say) is followed by a whole sentence (a clause), you normally need the conjunction que to introduce that clause.

Mi hermana dice que debería dormir más.
= My sister says (that) I/she should sleep more.

In English, that can be dropped: My sister says I should sleep more.
In Spanish, que usually cannot be dropped in this structure; Mi hermana dice debería dormir más sounds wrong.

Who is the one that “should sleep more”—me or my sister?

Grammatically, debería is ambiguous by itself because Spanish often drops subject pronouns:

yo debería (I should)
ella debería (she should)

In Mi hermana dice que debería dormir más, pero siempre se acuesta tarde, the second part:

pero siempre se acuesta tarde = but she always goes to bed late

clearly refers to my sister (3rd person singular: se acuesta).
So the most natural interpretation is:

My sister says she should sleep more, but she always goes to bed late.

If you wanted to make it 100% explicit, you could say:

Mi hermana dice que ella debería dormir más… (she should)
Mi hermana dice que yo debería dormir más… (I should)

What form is debería? Is it a tense, and what does it express?

Debería is the conditional form of deber (to have to / should), 3rd person singular (or 1st person singular — same form):

yo debería = I should / I ought to
él / ella debería = he / she should / ought to

The conditional of deber is commonly used for:

soft advice / recommendation
- Deberías estudiar más. = You should study more.
milder, less forceful obligation than debe or tiene que.

So debería dormir más = should sleep more (advice, not a strong order).

Why is it debería dormir and not debería duermo?

When deber (or debería) is used in the sense of should / ought to, it is followed by an infinitive:

deber + infinitive
- Debo dormir. = I must / should sleep.
- Deberías comer. = You should eat.
- Debería dormir más. = (He/She/I) should sleep more.

So dormir stays in the infinitive, not conjugated to duermo.

Why is it dormir más and not más dormir?

In Spanish, más (more) usually goes:

before adjectives/adverbs:
- más rápido = faster
- más cansado = more tired
after verbs when it means “more [of this action]”:
- trabajar más = to work more
- comer más = to eat more
- dormir más = to sleep more

So dormir más is the natural word order: verb + más.
más dormir would sound odd or need a special context to make sense.

What does se do in se acuesta?

Acostarse is a reflexive verb, meaning literally “to put oneself to bed / to lie oneself down”, and in practice it means “to go to bed”.

Infinitive: acostarse
Reflexive pronouns: me, te, se, nos, se

So:

Yo me acuesto. = I go to bed.
Ella se acuesta. = She goes to bed.

Here, se is the reflexive pronoun for ella (or él / usted), required by the verb.

Why is it se acuesta and not just acuesta?

Without the reflexive se, acostar means “to put someone else to bed”:

Yo acuesto a mi hijo. = I put my son to bed.

With se, acostarse means “to go to bed (oneself)”:

Mi hermana se acuesta tarde. = My sister goes to bed late.

Since your sister is going to bed herself, you must use the reflexive form: se acuesta.

Why does acostar become acuesta? Where does the ue come from?

Acostar is a stem‑changing verb (o → ue) in the present tense for most forms:

yo acuesto
tú acuestas
él / ella / usted acuesta
ellos / ellas / ustedes acuestan

But:

nosotros / nosotras acostamos (no change)
vosotros / vosotras acostáis (no change — mostly in Spain)

So in se acuesta, the root vowel o changes to ue as part of regular present‑tense conjugation: acostar → acuesta.

Why is there no ella in siempre se acuesta tarde?

Spanish often omits subject pronouns because the verb ending already shows the subject:

se acuesta = clearly he/she/it/usted goes to bed

So:

Ella siempre se acuesta tarde.
Siempre se acuesta tarde.

Both mean the same; the second just drops ella because it’s understood from context and the verb form.

What does tarde mean here—“afternoon” or “late”?

In this sentence, tarde is an adverb meaning late:

Se acuesta tarde. = She goes to bed late.

When talking about the time of day, la tarde (with article, usually) is the afternoon:

Por la tarde = in the afternoon.

Here there is no article and it’s used as an adverb, so it means late, not “afternoon”.

Could I say Mi hermana dice debería dormir más without que?

No. When decir is followed by a full clause, Spanish normally requires que:

correct: Mi hermana dice que debería dormir más.
incorrect / very unnatural: Mi hermana dice debería dormir más.

Spanish doesn’t allow dropping que in this structure the way English can drop that.

What is the difference between Mi hermana dice que debería dormir más and Mi hermana me dice que debería dormir más?

Mi hermana dice que debería dormir más.
- My sister says (that) [someone] should sleep more.
- General statement; no direct object. Context decides who “should sleep more”.
Mi hermana me dice que debería dormir más.
- My sister tells me that I should sleep more.
- me = to me; it makes it clear she is talking to me, and usually implies I am the one who should sleep more.

Adding me turns it into “she tells me” instead of just “she says”.

Could we use debe or tiene que instead of debería? What would change?

Yes, but the nuance changes:

Mi hermana dice que debe dormir más.
- My sister says she must / has to sleep more.
- Sounds stronger, more like an obligation.
Mi hermana dice que tiene que dormir más.
- My sister says she has to sleep more.
- Also a fairly strong obligation or necessity.
Mi hermana dice que debería dormir más.
- My sister says she should sleep more.
- Softer, more like advice or a recommendation.

So debería is the most “polite/advisory” of the three.

Why is there a comma before pero?

Spanish punctuation normally places a comma before “pero” when it introduces a contrasting clause, similar to English:

Mi hermana dice que debería dormir más, pero siempre se acuesta tarde.

First clause: what she says (she should sleep more).
Second clause: the contrast (she actually goes to bed late).
The comma marks this contrast clearly.