Breakdown of Können Sie den Dieb beschreiben, der die Waffe hat?
Sie
you (formal)
haben
to have
können
can / to be able to
der
who, which, that (relative pronoun; die, das)
Questions & Answers about Können Sie den Dieb beschreiben, der die Waffe hat?
Why is the relative pronoun der here when the first part says den Dieb?
The relative pronoun gets its gender (masculine) and number (singular) from the noun it refers back to, which is der Dieb. However, its case depends on its job in its own part of the sentence! In the relative clause, the thief is the subject (the one doing the having), so we use the nominative case der. It does not matter that he was the accusative object (den Dieb) in the main sentence.
Why is the verb hat at the very end instead of right after der?
A relative clause is a type of subordinate clause, and subordinate clauses in German always kick the conjugated verb to the very end. So instead of the normal word order where the verb is in the second position, the verb hat gets pushed all the way to the end, giving us der die Waffe hat.
Does der usually just mean the word the? How do I know it means who here?
You are right! The definite articles (der, die, das) do double duty in German. They are also used as relative pronouns meaning who, which, or that. You can tell it is a relative pronoun here because it comes right after a comma, refers back to a noun from the first half of the sentence, and pushes the verb to the end.
Is the comma before der required?
Yes! In English, we do not always use commas before who or that, but German grammar is very strict about this. You must always use a comma to separate the main sentence from a relative clause.