Relative pronouns combine the main clause with a subordinate clause. For example,
Ecco il libro che ti ho prestato.
Here’s the book that I lent you.
A. The most common relative pronoun in Italian is che. It is invariable and refers to both people and things. It can be the subject or object of a clause.
La camicia che (= soggetto) è sul letto non è stirata. The shirt on the bed isn’t ironed.
La camicia che (= oggetto) hai messo non è stirata. The shirt that you put on the bed isn’t ironed.
Lei è la ragazza che ho visto ieri. = She is the girl whom I saw yesterday.
Il cellulare che abbiamo è vecchio. = The cell phone that we have is old.
B. The relative pronoun cui can refer to people or things. It is invariable and is usually preceded by a simple preposition (a, di, con, da, ecc.). E.g.,
Il libro di cui mi hai parlato non mi è piaciuto.
I didn’t like the book that you talked to me about.
I due studenti con cui abito sono molto disordinati.
The two students with whom I live are very sloppy.
Quel bambino a cui hai restituito la palla è mio nipote.
The boy to whom you gave the ball is my nephew.
C. The relative pronoun il quale is a more formal relative pronoun (you will see it in written Italian more often than you will hear it in spoken Italian). It can replace che or cui. It may be employed when the use of che or cui would have ambiguous meaning. The appropriate form (il quale/ la quale/ i quali/ le quali) will agree in gender and number with the noun to which it refers (the antecedent):
Il ragazzo il quale mi ha telefonato è mio nipote.
The boy who called me is my nephew.
Ecco la casa nella quale è nato.
Here’s the house in which he was born.
D. The relative pronoun chi refers to people unspecifically (similar to the English “he/she who...” or “one who...”). It is often used in proverbs. It is always singular and masculine in form, but not in meaning. It is always used with the 3rd-person singular form of the verb:
Chi dorme non piglia pesci. = He who sleeps doesn’t catch fish.
Chi tace acconsente. = He who remains silent gives his consent.