A relative clause adds information about a noun: the man who lives here. German does this with a pronoun that looks exactly like the definite article, and one rule that decides its form.
Das ist der Mann, der hier wohnt. — That is the man who lives here.
Three things are happening: der appears twice with different jobs, the verb has gone to the end, and there is a comma. All three are compulsory.
The rule that decides the pronoun
Gender and number come from the noun it refers to. Case comes from its job inside the relative clause.
That split is the whole difficulty, and it is worth reading twice. The noun outside decides masculine or feminine. The clause inside decides nominative, accusative or dative.
Das ist der Mann, den ich kenne. — That is the man whom I know.
Mann is masculine, so the pronoun is masculine. But inside the clause, ich is the subject and the man is the object — so it is accusative, and masculine accusative is den.
The forms
| masculine | feminine | neuter | plural | |
|---|---|---|---|---|
| nominative | der | die | das | die |
| accusative | den | die | das | die |
| dative | dem | der | dem | denen |
| genitive | dessen | deren | dessen | deren |
These are the definite articles with two exceptions: denen in the dative plural and the whole genitive row. Everything else you already know from German cases.
Three sentences, one noun, three pronouns
Same man, three different jobs inside the clause.
| Sentence | Job inside the clause | Pronoun |
|---|---|---|
| der Mann, der hier wohnt | he lives — subject | nominative der |
| der Mann, den ich kenne | I know him — object | accusative den |
| der Mann, dem ich helfe | I help him — dative verb | dative dem |
The third one is dative because helfen takes a dative object, not because of anything about the sentence outside. If you know the verb, you know the pronoun.
The verb goes to the end
A relative clause is a subordinate clause, so it obeys the same rule as weil and dass.
Ich lese das Buch, das mein Freund mir gegeben hat.
— I am reading the book my friend gave me.
Both verbs pile up at the end, conjugated one last. German subordinate clauses covers why.
The comma is not optional. German still separates every relative clause with a comma, including the ones English would leave open. Das ist das Buch, das ich gelesen habe.
With a preposition
The preposition goes in front of the pronoun, and it chooses the case — exactly as it does anywhere else.
Das ist der Tisch, auf dem das Buch liegt. — That is the table the book is lying on.
Das ist der Freund, mit dem ich spiele. — That is the friend I play with.
German cannot strand the preposition at the end the way English does. There is no der Freund, den ich spiele mit. It moves to the front with the pronoun, always. Which case it forces is in German prepositions.
was, for when there is no noun
If the relative clause refers to a whole idea rather than a specific noun, use was.
Er ist zu spät gekommen, was mich geärgert hat. — He arrived late, which annoyed me.
Also after alles, nichts, etwas and das:
Das ist alles, was ich weiß. — That is everything I know.
welcher — the one you can ignore
You will meet welcher / welche / welches used as a relative pronoun in older or very formal writing. It means exactly the same thing and is declined the same way. Nobody uses it in speech, and you never need to produce it.
What to actually memorise
The split: gender from outside, case from inside. Then denen for dative plural, because it is the one form that is not simply the article you already know.
Rules stick faster once you have met the words. Every example above links to its own page.
Practise in the trainer