Who, which: the relative pronoun qui

Qui, quae, quod is the Latin who, which and that, and it is the eighth commonest word in the language. One rule runs it: gender and number from the noun it refers to, case from its own clause. Here it is on one noun, rex, in five jobs.

The noun outside, rex, never changed. The pronoun did, because its job changed.

The forms

Like is, hic and ille, it has a genitive in -ius and a dative in -i for every gender: cuius, cui. Much of the rest runs close to bonus, bona, bonum.

Gender from outside, case from inside

Ask two questions, in this order:

1. Which noun does it refer to? That gives gender and number.
2. What does it do in its own clause? That gives the case.

A whole sentence, for the shape of it:

• Vir quem vides frater meus est. - The man whom you see is my brother.

Vir is the subject of est; quem is the object of vides. Two clauses, two cases, one man.

quae does three jobs

The commonest trap. Quae is the feminine singular, the feminine plural and the neuter plural:

The verb usually settles the number, and the dictionary settles the gender: verbum, verbi is neuter, so its plural takes quae, never quas. And a noun whose ending hides its gender still takes the matching form: liber, libri, book, is masculine, so liber qui in templo est, the book which is in the temple.