Der erwachsene Sohn arbeitet.

Der is the definite article in German, like the in English.

In this sentence, der shows that Sohn is:

• masculine
• singular
• in the nominative case (the subject of the sentence)

So der Sohn = the son.

Because Sohn is the one doing the action, German uses the nominative form der.

Because the adjective has to take an ending that matches the noun phrase.

Here, erwachsene describes Sohn, and it comes after the definite article der. In German, adjective endings depend on:

• gender
• number
• case
• what kind of article comes before the noun

In der erwachsene Sohn:

• der = masculine, singular, nominative
• after a definite article, the adjective takes the weak ending
• for masculine nominative singular, that weak ending is -e

So:

• der erwachsene Sohn = correct

Compare:

• ein erwachsener Sohn = an adult son

Here the adjective changes to erwachsener because ein does not show all the grammatical information as clearly as der does.

In German, all nouns are capitalized.

So:

• Sohn is a noun, so it gets a capital letter
• erwachsene is an adjective here, so it stays lowercase

Also, Der is capitalized here only because it is the first word of the sentence. If it appeared in the middle of a sentence, it would normally be der.

It is in the nominative case.

You can tell because it is the subject of the sentence — the person doing the action:

• The adult son works.

In German, the subject is usually in the nominative case. The article der is also a clue, because der is the nominative masculine singular form of the.

Arbeitet is in the present tense.

It comes from the verb arbeiten, which means to work.

So:

• ich arbeite = I work / I am working
• du arbeitest = you work / you are working
• er/sie/es arbeitet = he/she/it works / is working

In this sentence, der erwachsene Sohn arbeitet means:

• The adult son works or
• The adult son is working

German present tense often covers both of those English meanings.

It actually is the -t ending for er/sie/es, but there is an extra -e- before it because of pronunciation.

The verb is arbeiten. Its stem is arbeit-. If German added only -t, the result would be hard to pronounce: arbeitt.

So German inserts an extra -e-:

• arbeit-et

This happens with many verbs whose stems end in -t or -d:

• arbeiten → er arbeitet
• reden → er redet
• finden → du findest (not exactly the same pattern in every form, but similar pronunciation issues matter)

It can mean both, depending on context.

German usually uses the simple present tense where English might use either:

• works
• is working

So Der erwachsene Sohn arbeitet could mean:

• The adult son works
  or
• The adult son is working

If there is no extra context, English speakers often choose whichever sounds more natural in the situation.

Yes, and that means something slightly different in structure.

• Der erwachsene Sohn arbeitet.
  = The adult son works.
  Here, erwachsene is an attributive adjective directly in front of the noun.

• Der Sohn ist erwachsen.
  = The son is adult / grown-up.
  More natural English: The son is an adult.
  Here, erwachsen comes after sein and acts as a predicate adjective.

Notice the form change:

• before the noun: der erwachsene Sohn
• after ist: der Sohn ist erwachsen

When the adjective is used after sein, it usually does not take an ending.

Because German main clauses usually follow the verb-second rule, often called V2.

In a normal statement, the finite verb goes in the second position:

• Der erwachsene Sohn arbeitet.

Here:

1. Der erwachsene Sohn = first element
2. arbeitet = second element

Even if you move another element to the front, the verb still stays second:

• Heute arbeitet der erwachsene Sohn.
  = Today the adult son is working.

This is a very important German word order rule.

In a yes/no question, German usually puts the finite verb first:

• Arbeitet der erwachsene Sohn?
  = Is the adult son working? / Does the adult son work?

So compared with the statement:

• Der erwachsene Sohn arbeitet.

the verb moves to the front:

• Arbeitet der erwachsene Sohn?

The plural would be:

• Die erwachsenen Söhne arbeiten.
  = The adult sons work / are working.

Notice the changes:

• der → die
• erwachsene → erwachsenen
• Sohn → Söhne
• arbeitet → arbeiten

This shows how article, adjective, noun, and verb can all change depending on number.

A simple learner-friendly pronunciation is:

• er-WAKH-suh-nuh

A few helpful notes:

• the w in German sounds like English v
• ch here is the softer German ch sound, not an English k
• the final -e in erwachsene is pronounced, roughly like a light uh

And Sohn is pronounced roughly like:

• zohn

where z sounds like the z in English zoo, and oh is a long vowel.