Learn Hardcore Spanish (Latin America): Hay que dormir bien antes de un examen importante. - One must sleep well before an important exam.

“hay” comes from the verb haber, used here in an impersonal form.
“que” is just a connector that always follows this “hay” in this structure.
It is always followed by an infinitive verb: hay que dormir, hay que estudiar, hay que comer, etc.
It does not have a personal subject (no “I/you/we”): it’s about people in general.

So “Hay que dormir bien…” means something like “People should sleep well…” / “One should sleep well…” without saying exactly who.

How is “hay que” different from “tener que” or “deber”?

All three can express obligation, but they’re used differently:

hay que + infinitive
- Impersonal, general rule.
- No subject.
- Example: Hay que dormir bien. = You/people should sleep well (in general).
tener que + infinitive
- Personal, with a subject.
- Conjugate tener for the person.
- Example:
  - Tengo que dormir bien. = I have to sleep well.
  - Tenemos que dormir bien. = We have to sleep well.
deber + infinitive
- Also personal, with a subject.
- Often sounds a bit more like “should/ought to” (moral/strong recommendation).
- Example:
  - Debo dormir bien. = I should sleep well.
  - Debemos dormir bien. = We should sleep well.

So in your sentence, “Hay que dormir bien…” is a general recommendation, not tied to a specific person.

Who is the subject in “Hay que dormir bien”? Who actually has to sleep well?

Grammatically, there is no real subject in that sentence.

“Hay” is impersonal (like English “it” in It’s raining — there’s no real “it”).
The sentence is talking about people in general: anyone who will take an important exam.

So the idea is:

“People have to sleep well before an important exam.”
“You (in general) should sleep well before an important exam.”

But Spanish doesn’t name the subject here; it uses the impersonal “hay que” instead.

Why is “dormir” in the infinitive form and not conjugated like “duermo” or “dormimos”?

In the structure “hay que + infinitive”, the verb must be in the infinitive:

Hay que dormir.
Hay que estudiar.
Hay que comer.

You cannot conjugate the verb after “hay que”:

❌ Hay que duermo.
✅ Hay que dormir.

The infinitive here works almost like “to sleep / sleeping” in English:

Hay que dormir bien.
≈ It’s necessary to sleep well / Sleeping well is necessary.

Why is it “dormir bien” and not “dormir bueno”?

This is about adverbs vs adjectives:

bien = well → adverb (describes how you do something).
bueno / buena = good → adjective (describes a noun).

In “dormir bien”:

“dormir” is a verb (to sleep).
We want to describe how you sleep → we need an adverb → bien.

So:

✅ Dormir bien = to sleep well (correct).
❌ Dormir bueno = to sleep good (ungrammatical in Spanish, like in English).

Examples:

Comer bien es importante. = Eating well is important.
Una comida buena. = A good meal.
(Here buena describes the noun comida, so the adjective is correct.)

What does “antes de” mean here, and why do we need the “de”?

“Antes de” is a prepositional phrase meaning “before” when followed by a noun or an infinitive verb.

In your sentence:

antes de un examen importante = before an important exam.

The “de” is required because:

antes by itself normally works as an adverb (“before/earlier”), not directly before a noun.
When you want “before + noun / verb”, you use:
- antes de + noun → antes de un examen (before an exam)
- antes de + infinitive → antes de estudiar (before studying)

Examples:

Antes, no dormía bien. = Before, I didn’t sleep well. (no “de”; antes is on its own)
Antes de la clase, tomo café. = Before class, I drink coffee.
Antes de dormir, leo. = Before sleeping, I read.

Why is it “un examen importante” and not “el examen importante”?

This is about indefinite vs definite articles:

un = a / an (non-specific, any example of that thing)
el = the (specific, known thing)

In “antes de un examen importante”:

“un examen importante” means “an important exam (any important exam)”, speaking generally.
The sentence is about a general situation: what people should do before any important exam.

If you say “el examen importante”, you’re talking about a specific exam that both speaker and listener already know about:

Hay que dormir bien antes del examen importante.
= One must sleep well before the important exam (the particular one we already know about, e.g., your final tomorrow).

So with “un”, the advice is general; with “el”, it’s about a specific exam.

Why is the adjective “importante” after “examen”, and can it go before the noun?

In Spanish, the default position for adjectives that describe a quality is after the noun:

un examen importante = an important exam
(literally: an exam important)

This is the most neutral, usual word order.

Can it go before?

un importante examen is grammatically possible, but it:
- sounds more formal / literary, and
- often gives a bit more emphasis or a stylistic feel.

In everyday speech in Latin America, people almost always say:

✅ un examen importante

Other examples of typical noun + adjective order:

un libro interesante = an interesting book
una ciudad grande = a big city

How could I say the same idea but talking specifically about myself (or someone else), not people in general?

To make it personal, you usually switch from “hay que” to “tener que” or “deber”, and you conjugate for the subject.

For “I have to”:

Tengo que dormir bien antes de un examen importante.
= I have to sleep well before an important exam.

For “You (tú) have to”:

Tienes que dormir bien antes de un examen importante.

For “We have to”:

Tenemos que dormir bien antes de un examen importante.

Using “deber” (more like “should/ought to”):

Debo dormir bien antes de un examen importante. = I should sleep well…
Debemos dormir bien antes de un examen importante. = We should sleep well…

The rest of the sentence (dormir bien antes de un examen importante) stays the same; only the expression of obligation changes.

Can I change the word order to “Antes de un examen importante, hay que dormir bien”? Does it sound natural?

Yes, that word order is perfectly natural and very common:

Antes de un examen importante, hay que dormir bien.

Moving “antes de un examen importante” to the beginning:

Slightly emphasizes the time frame (before an important exam).
Does not change the basic meaning.

Both are good, natural sentences in Latin American Spanish:

Hay que dormir bien antes de un examen importante.
Antes de un examen importante, hay que dormir bien.