Gender from outside, case from inside

A relative clause modifies a noun (the antecedent) and is introduced by a relative pronoun (der/die/das or welcher/welche/welches). The relative pronoun agrees with the antecedent's gender (masculine/feminine/neuter/plural) and takes a case determined by the verb or preposition inside the relative clause. The conjugated verb goes to the end of the relative clause, just like all subordinate clauses: "Der Mann, den ich gestern getroffen habe, ist mein Lehrer." Relative clauses are always set off by commas.

Almost. In the nominative, accusative, and dative singular and most plural forms, the relative pronouns der/die/das are identical to the definite articles. The forms diverge only in the genitive (dessen for masculine/neuter singular, deren for feminine singular and all plurals) and in the dative plural (denen instead of den). Because most forms match the article, learners who know their articles already know most of the relative-pronoun table.

"dessen" is the genitive relative pronoun for masculine and neuter singular antecedents; "deren" covers feminine singular and all plurals. Both translate to English "whose" and signal that the relative pronoun is the genitive possessor of a noun inside the relative clause: "der Mann, dessen Auto rot ist" (the man whose car is red — masculine antecedent), "die Frau, deren Tasche gestohlen wurde" (the woman whose bag was stolen — feminine antecedent). These are the only relative-pronoun forms that do not match the definite article.

Both forms are grammatically correct and interchangeable. "welcher/welche/welches" is the more formal and literary alternative; it is occasionally preferred in writing when "der/die/das" would appear directly next to a definite article and create visual ambiguity: "die Studenten, welche/die hier wohnen." In spoken German, "der/die/das" is used almost exclusively. Most B1 learners can focus on recognising "welcher" and producing "der/die/das".

The preposition that governs the relative pronoun's case sits before the pronoun inside the relative clause, not stranded at the end as in English. "der Mann, mit dem ich spreche" (the man with whom I speak — not "the man I speak with"). The case of the relative pronoun follows the preposition's normal government: "mit" → dative → "dem"; "für" → accusative → "den"; "von" → dative → "dem".

For geographic places (cities, countries, regions) "wo" is the more idiomatic relative: "Berlin, wo ich wohne" instead of "Berlin, in dem ich wohne." Both are grammatically correct; "wo" flows better for place names. The same pattern extends to "wohin" (destination) and "woher" (origin): "die Stadt, wohin er gezogen ist."

"was" follows universal/indefinite antecedents: alles (everything), etwas (something), nichts (nothing), vieles (many things), manches (some things), and also "das" used as a placeholder for a whole preceding clause: "Er sagt nichts, was wir nicht wissen." "wer" introduces relative clauses without an explicit antecedent ("whoever"): "Wer A sagt, muss auch B sagen."

By commas — one before the relative pronoun and one after the closing verb of the relative clause. The main clause's verb (and any continuation) resumes after the second comma: "Der Mann, der gestern angekommen ist, ist mein Onkel." If the relative clause is appended at the end of the main clause, only the opening comma is needed.