Learn Hardcore German: Das Kind muss sich heute ausruhen.

The basic verb is sich ausruhen = to rest (oneself), to take a rest.
With reflexive verbs, the action reflects back onto the subject:
- Ich ruhe mich aus. – I rest (myself).
- Du ruhst dich aus.
- Das Kind ruht sich aus.

Without sich, ausruhen would either sound incomplete or mean something different (like to rest something), which is rare and not what is meant here.

So muss sich ausruhen = has to rest (itself) → has to rest.

Why is the reflexive pronoun sich and not something else?

Reflexive pronouns in German change with person and number. For the 3rd person singular (he, she, it / er, sie, es), the reflexive pronoun is always sich, no matter the gender:

Er ruht sich aus.
Sie ruht sich aus.
Es / Das Kind ruht sich aus.

In our sentence, das Kind is grammatically third person singular (like es), so we use sich:

Das Kind muss sich heute ausruhen.

Why is ausruhen at the very end of the sentence?

Because of the modal verb muss.

In German, when you have a modal verb (like müssen, können, wollen, dürfen, sollen, mögen) plus another verb, the modal is conjugated and goes in the second position, and the main verb stays in the infinitive at the end:

Das Kind muss sich heute ausruhen.
- muss = 2nd position (conjugated)
- ausruhen = at the end (infinitive)

If you don’t use a modal verb, then ausruhen behaves like a normal separable verb:

Das Kind ruht sich heute aus. (present tense without modal)

Is ausruhen a separable verb? How would it look in a simple present tense sentence?

Yes, ausruhen is a separable verb: aus (prefix) + ruhen (base verb).

In a normal present tense main clause (no modal verb), the prefix separates and goes to the end:

Das Kind ruht sich heute aus.
- ruht = conjugated part in 2nd position
- aus = separable prefix at the end

But with a modal verb (muss), the verb stays in one piece as an infinitive at the very end:

Das Kind muss sich heute ausruhen.

What is the role of muss here, and why is it spelled like that?

Muss is the 3rd person singular form of the modal verb müssen (to have to, must).

Conjugation in the present tense:

ich muss
du musst
er/sie/es muss
wir müssen
ihr müsst
sie/Sie müssen

So with das Kind (3rd person singular), we need muss:

Das Kind muss sich heute ausruhen.
→ The child has to rest today.

What case is das Kind in, and why?

Das Kind is in the nominative case because it is the subject of the sentence – the one that has to rest.

Subject (nominative): Das Kind
Verb: muss sich ausruhen

If we changed the sentence and added an object, that object would usually be in accusative or dative, but here we only have the subject and a reflexive pronoun.

Why is Kind capitalized?

In German, all nouns are capitalized, no matter where they appear in the sentence.

das Kind – the child
heute is not capitalized because it’s an adverb, not a noun.
Even in the middle of sentences, nouns stay capitalized:
- Das Kind muss sich heute ausruhen.
- Ich sehe das Kind.

What does heute do here, and where can it go in the sentence?

Heute means today. It’s a time adverb telling us when the child has to rest.

In the given sentence, it stands in the “middle field” before the infinitive:

Das Kind muss sich heute ausruhen.

You have some flexibility:

Das Kind muss heute sich ausruhen. (possible, sounds a bit less neutral)
Heute muss sich das Kind ausruhen. (emphasis on “today”)
Das Kind muss sich ausruhen heute. (possible in spoken language, but less standard)

The most neutral and typical versions are:

Das Kind muss sich heute ausruhen.
Heute muss sich das Kind ausruhen.

Could you leave out heute? Would the sentence still be correct?

Yes. Heute is optional.

Das Kind muss sich ausruhen.
→ The child has to rest.

This is grammatically fully correct; you just lose the information that it has to happen today.

Can you say Das Kind muss heute ausruhen without sich?

Native speakers would almost always include sich when they mean to rest:

Das Kind muss sich heute ausruhen. ✅ (natural)

Without sich, ausruhen is either:

interpreted as incomplete, or
understood in a more unusual, transitive sense (to rest something), which is rarely used.

So for the everyday meaning to rest, you should treat it as sich ausruhen and keep the reflexive pronoun.

Is this sentence only present tense, or can it also refer to the future?

Grammatically it is present tense (Präsens):

Das Kind muss sich heute ausruhen.

However, German often uses the present tense to talk about the near future, especially when there is a time expression like heute:

It can mean: The child has to rest today (later today, not necessarily right now).

Context and heute make it clear that it’s about today, which can be now or later today.

What would the sentence look like in the simple past (Präteritum) without a modal verb?

Without a modal verb, you use ruh(en) in the simple past and keep the verb separable:

Present: Das Kind ruht sich heute aus.
Simple past: Das Kind ruhte sich gestern aus. (yesterday instead of today)

If you keep the modal verb and move to the simple past of müssen, then muss → musste, and ausruhen stays in the infinitive at the end:

Das Kind musste sich gestern ausruhen.
→ The child had to rest yesterday.

Is there a difference between sich ausruhen and sich erholen?

Yes, there is a nuance:

sich ausruhen
- Very common, everyday.
- Means simply to rest, to take a break, to relax for a while.
- Often short-term.
- Das Kind muss sich heute ausruhen.
sich erholen
- Can sound a bit more formal, often used for recovery from illness, stress, work, etc.
- More like to recover, to recuperate.
- Das Kind muss sich nach der Krankheit erholen.

In your sentence, sich ausruhen is the natural choice for having a rest today.