146. A connecting pronoun referring to something which precedes (or
follows) is called a "relative pronoun". The person or thing to which
it refers is called its "antecedent." The relative pronoun, identical
in form with the interrogative pronoun (106), as in English, is "kiu",
which, who.
[Footnote: Sometimes English uses "that" for a relative pronoun, as
"I saw the book that you have." This must always be translated by
"kiu". Likewise, English sometimes omits the relative pronoun, as "I
saw the book you have." The relative pronoun is never thus omitted in
Esperanto.]
The relative pronoun agrees in number with its antecedent. Whether it
is in the accusative case or not depends upon its relation to its own
verb or to other words in its own clause (called the relative clause):
La junuloj, kiuj venis, estas afablaj,
the youths who came are amiable.
La personoj, kiujn li vidos, estas amikoj miaj,
the persons (whom) he will see are friends of mine.
Mi kalkulis la gradon, kiun li ricevos,
I calculated the grade (which) he will receive.
Mi memoras tiun aferon, pri kiu vi parolas,
I remember that matter about which you speak.
147. Like English "whose" the genitive form "kies" of the interrogative
pronoun (107) is also used as a relative, referring to a substantive
(singular or plural) for its antecedent:
Li estas la viro, kies libron vi trovis,
he is the man whose book you found.
Mi konas la infanojn, kies patro estas amiko via,
I know the children whose father is a friend of yours.