Relative pronouns

Relative pronouns are commonly used to combine two sentences that have the same noun or pronoun in both. One of them is changed to a relative pronoun, and the sentences are then combined:

identical noun + identical noun
Do you know the man? + The man is a thief.
Do you know the man, who is a thief?
Two types of relative pronouns

  In German, there are two basic types of relative pronouns. One is formed from the definite article, and the other is formed from the der-word welcher. Naturally, in German you have to consider the gender, number, and case when using relative pronouns. Let’s look at their declension:
                             Masculine    Feminine    Neuter     Plural

Definite article
Nominative:       der                die                das            die
Accusative:         den               die                das            die
Dative:                dem              der                dem          denen
Possessive:         dessen         deren           dessen       deren
Welcher
Nominative:       welcher       welche         welches     welche
Accusative:         welchen      welche         welches     welche
Dative:                welchem     welcher        welchem   welchen
Possessive:         dessen         deren            dessen       deren
Notice that both the definite article form and the welcher form have the identical possessive adjective where the genitive case would normally occur.
    Just like English relative pronouns, German relative pronouns combine two sentences that have the same noun or pronoun in both. But in German, gender, number, and case must be considered. If the noun replaced by a relative pronoun is nominative, the relative pronoun must be nominative. For example:

Der Junge ist Amerikaner. Der Junge lernt Deutsch. 
The boy is an American. The boy is learning German.
Der Junge, der Deutsch lernt, ist Amerikaner.

The boy, who is learning German, is an American.

Wo sind die Kinder? Die Kinder spielen Schach.
Where are the children? The children are playing chess.
Wo sind die Kinder, die Schach spielen?
Where are the children who are playing chess?
main clause +  der/die/das + relative clause with verb in final position
Das ist der Mann, + der + unser Haus kaufte.
That’s the man who bought our house.
main clause + welcher + relative clause with verb in final position
Das ist der Mann, + welcher + unser Haus kaufte.
That’s the man who bought our house.
If the noun replaced by a relative pronoun is accusative, the relative pronoun must be accusative. For example:
Sie ist die Frau. Thomas liebt die Frau.               She is the woman. Thomas loves the woman.
Sie ist die Frau, die Thomas liebt.                         She is the woman that Thomas loves.
Sie ist die Frau, welche Thomas liebt.

Er sprach mit dem Herrn. Niemand kennt            He spoke with the gentleman. No one                    den Herrn.                                                                   knows the gentleman.
Er sprach mit dem Herrn, den niemand                He spoke with the gentleman whom no one
kennt.                                                                             knows.
Er sprach mit dem Herrn, welchen
niemand kennt.
If the noun replaced by a relative pronoun is dative, the relative pronoun must be dative. For
example:
Kennst du die Leute? Er spricht mit den            Do you know the people? He is talking to        Leuten.                                                                     the people.
Kennst du die Leute, mit denen er spricht?       Do you know the people that he is talking to?
Kennst du die Leute, mit welchen er
spricht?
Die Dame ist eine Verwandte. Er hilft                   The lady is a relative.He helps the lady.
der Dame.
Die Dame, der er hilft, ist eine Verwandte.          The lady that he helps is a relative.
Die Dame, welcher er hilft, ist eine
Verwandte.

If the noun replaced by a relative pronoun is in the genitive case or is a possessive adjective, the relative pronoun must be in the possessive adjective form. For example:

Er sieht den Lehrer. Die Schüler des          He sees the teacher. The teacher’s students are
Lehrers singen ein Lied.                                singing a song.
Er sieht den Lehrer, dessen Schüler ein    He sees the teacher, whose students are singing
Lied singen.                                                      a song.
Das ist die Richterin. Ihr Sohn wurde                    That’s the judge. Her son was arrested.
verhaftet.
Das ist die Richterin, deren Sohn verhaftet          That’s the judge whose son was arrested.
wurde.
In the last example, the possessive adjective ihr refers to the noun Richterin and therefore is
replaced by the corresponding feminine, singular relative pronoun.

  It is probably wise to remind you that English has three types of relative pronouns: (1) who

and which, which introduce a non-restrictive relative clause that gives parenthetical information; (2) that, which introduces a restrictive relative clause that helps to define the antecedent; and (3) an elliptical relative pronoun, which is understood but not spoken or written. All three types of English relative pronouns can be translated into German by the German definite article or welcher. For example:

Der Mann, den ich sah, ist ein Freund.                  The man, whom I saw, is a friend.
                                                                                        The man that I saw is a friend.
                                                                                        The man I saw is a friend.
When the case of a German relative pronoun is determined by its accompanying preposition, the preposition precedes the relative pronoun. The position of a preposition in an English relative clause is more flexible. For example:
Das ist der Mann, für den er arbeitet.                    That’s the man for whom he works.
That’s the man that he works for.
That’s the man he works for.
Wo ist die Dame, mit der ich sprach?                    Where’s the woman with whom I spoke?
Where’s the woman that I spoke with?
Where’s the woman I spoke with?

Wer and der

There is another aspect to relative pronouns. When no specific person is referred to in a sentence, the pronoun wer is used as a relative pronoun. It is usually paired with der, and the English meaning of this concept is he, who, or who(so)ever. For example:

He who lies about me is no friend of mine.
Whoever threw that snowball is in a lot of trouble.

Since German declines words like wer and der, this kind of relative pronoun usage can appear in all the cases:

Wer oft lügt, den respektiert niemand.               He who often lies is respected by no one.
Wen die Polizei verhaftet, dem kann man          No one can help him, whom the police arrest.

nicht helfen. 
Wem das imponiert, der ist wohl naiv.                Whomever that impresses is probably naive. 

Wessen Brot man isst, dessen Lied man singt.  If you eat his bread, you must dance to his
                                                                                      tune. (A saying)

You will notice that the declension of wer and der is dependent upon the use of each in its own clause.