Relative clauses in German
A Relativsatz describes a noun by attaching a clause to it: Der Mann, der dort steht, ist mein Bruder. = The man who's standing there is my brother. The relative pronoun looks like the definite article (der, die, das, die) but with two surprises in the genitive (dessen, deren) and the dative plural (denen). Three things determine its form: (1) gender and number match the noun it refers to (the antecedent); (2) case comes from the role inside the relative clause itself (subject? direct object? prepositional?); (3) the verb goes to the END (subordinate clause). Plus two extras: was as a relative for indefinite antecedents (alles, etwas, nichts, das, plus a whole previous clause), and wo as a relative for places.
The relative pronoun table
Almost the definite article — but pay attention to the genitive and the dative plural. Masculine: der / den / dem / dessen. Feminine: die / die / der / deren. Neuter: das / das / dem / dessen. Plural: die / die / denen / deren. The order is nominative / accusative / dative / genitive. dessen, deren, denen, deren are the four to memorize — they're slightly different from the definite article (des, der, den, der). Whichever case role the noun plays INSIDE the relative clause, that's the case form you pick — independent of the noun's case in the main clause.
Picking the case — role inside the clause
Two-step rule: gender/number from the antecedent; case from the role inside the relative clause. Subject of the rel. clause → nominative. Der Mann, der dort steht, … (er steht → der). Direct object → accusative. Der Mann, den ich kenne, … (ich kenne ihn → den). Indirect object or after a dative verb → dative. Der Mann, dem ich helfe, … (ich helfe ihm → dem). Possession → genitive. Der Mann, dessen Auto rot ist, … = The man whose car is red, … The relative pronoun starts the relative clause; the verb goes to the end.
dessen and deren — 'whose'
Genitive relative pronouns mean 'whose'. dessen for masculine and neuter antecedents, deren for feminine and plural. Pattern: rel. pronoun + noun WITHOUT another article. Der Mann, dessen Auto kaputt ist, … = The man whose car is broken, … Die Frau, deren Tochter studiert, … = The woman whose daughter is studying, … Die Bücher, deren Autor ich kenne, … = The books whose author I know, … Note: NO article before the noun — dessen Auto, not dessen das Auto. The following noun's adjectives take strong endings (because dessen / deren don't show case for the noun): dessen netter Bruder, deren neue Wohnung.
Preposition + relative pronoun
When a relative is governed by a preposition, the preposition comes FIRST, the relative pronoun second, both at the start of the rel. clause. Der Mann, mit dem ich gesprochen habe, … = The man with whom I spoke / I spoke to, … Das Buch, in dem ich lese, … = The book I'm reading. Der Stuhl, auf dem du sitzt, … = The chair you're sitting on. The case after the preposition follows the preposition's normal rules: mit + dat → mit dem / mit der / mit denen. Two-way prepositions: pick dative for location, accusative for direction. German doesn't strand prepositions at the end the way English does — it lifts them up front.
was — relative for indefinite antecedents
Use was when the antecedent is an indefinite or abstract pronoun: alles, etwas, nichts, vieles, wenig, das. Alles, was ich brauche, ist Zeit. = All (that) I need is time. Es gibt etwas, was ich dir sagen muss. = There's something (that) I have to tell you. Das, was du gesagt hast, war richtig. = What you said was right. (lit. 'that, what you said'). was is also used to refer back to a WHOLE previous clause: Er hat den ganzen Tag geschlafen, was mich überrascht hat. = He slept the whole day, which surprised me. After superlatives + neuter, was is also standard: Das ist das Beste, was du tun kannst. = That's the best (thing) you can do.
wo — relative for places (and time)
wo can replace in dem / in der / in denen when referring to a place. Die Stadt, wo ich wohne, ist klein. = The city where I live is small. Das Land, wo ich geboren bin, ist Deutschland. = The country where I was born is Germany. With proper place names (cities, countries), wo is preferred: Berlin, wo ich wohne, … (NOT Berlin, in dem ich wohne). For other nouns, both wo and in dem / in der are acceptable. wo can also be used with time expressions in casual register: Der Tag, wo wir uns kennenlernten ('the day when we met') — though an dem is more formal.
Word order and commas
Always commas before AND after the relative clause (unless it's at the end of the sentence — then just the comma before). Verb of the rel. clause goes to the END. The relative clause sits as close to the antecedent as possible, ideally right after it: Der Mann, der dort steht, ist mein Bruder. Putting the relative clause far from its antecedent is allowed but harder to follow. With um zu or other infinitive complications, the relative clause stays one chunk before continuing. Long relative clauses can split between subject and verb of the main clause — German is fine with that, English isn't.
When NOT to use which one
Common mistakes to dodge: (1) Don't drop the relative pronoun. English allows 'the man (who) I saw'; German requires den every time. (2) Don't use was for a regular noun antecedent. Das Buch, was ich lese is wrong — use das Buch, das ich lese. (3) Don't use wo for non-places: der Tag, wo is colloquial; in writing, an dem. (4) Don't forget that dessen / deren govern the next noun directly with no article: dessen Bruder, not dessen der Bruder.
