To some German students, relative clauses in German are almost as mysterious as Einstein's theory of relativity 😜 And yet, when you have a good understanding of the cases, prepositions, and word order in subordinate clauses, then it is not a big leap to understand how relative clauses are used in the language. Let me explain why.
Relative clauses combine what you have learned about the cases and prepositions with the word order in a subordinate clause because relative clauses are a particular type of subordinate clause- one that seeks to provide further information about a noun. The key is to concentrate on the case of the noun which you're trying to describe within your relative clause. In the chart below, you will find the relative pronouns we use to form relative clauses, which largely correspond with the definite articles.
As the examples show, relative clauses combine two separate sentences and omit the noun which they are seeking to describe. Whenever you get confused on what your relative pronoun should be, just look at your relative clause in isolation, turn it back into the normal word order of a main clause and check which article you would give the noun. Watch out for the three exceptions, though. Dessen for masculine and neuter Genitive, deren for feminine and plural Genitive, and denen for Dative plural.
Since prepositions can affect your choice of relative pronoun, you should learn the two-way prepositions, as well as prepositions that only go with the accusative, dative, and genitive case. The last example in the above, where "was" is used to refer to a whole sentence, is also known as an indirect question in German.
Relative clauses are important as they are one of two ways in which nouns can be described in the German language- adjectives are the other. So make sure that you gain a good understanding of both topics as they will allow you to express yourself in a more nuanced manner.
Do you have other questions about German grammar? Then check out our German language blog "Auf Deutsch, bitte!", where you will find posts about the difference between the subordinate clause clause conjunctions um...zu and damit, as well as als and wenn; the pronouns mir and mich, man, and pronoun rules more generally; gender and plural rules in German; separable verbs and many other topics. We also have posts that might be of interest to those who learn other languages, such as an A-Z guide to grammar terminology, an explanation on the different language levels from A1 to C2, reviews of the most popular online dictionaries and language learning apps, and I offer some insights on how to learn vocabulary.