Formal relative pronouns (el cual)

In formal writing, bureaucratic procedures, and diplomatic affairs, you will often see el cual (and its variants) used to mean "which," "who," or "whom." While everyday speech usually relies simply on que, el cual adds precision and formality.

SingularPlural
Masculineel cuallos cuales
Femininela cuallas cuales

Agreeing with the noun

Like many Spanish pronouns, el cual must match the gender and number of the noun it refers back to.

For a masculine, singular noun like el tratado (the treaty), use el cual:

The treaty, which the president signed, is important.
El tratado, el cual firmó el presidente, es importante.

For a feminine, singular noun like la asamblea (the assembly), use la cual:

The assembly, which was organized by the government, starts now.
La asamblea, la cual fue organizada por el gobierno, empieza ahora.

And for plural nouns, use los cuales or las cuales:

They drafted those decrees, which they will issue tomorrow.
Redactaron esos decretos, los cuales emitirán mañana.
The institution issued the visas, which we were expecting.
La institución emitió las visas, las cuales esperábamos.

Using "el cual" with prepositions

One of the most common ways to use el cual is after prepositions (like sin, para, según, or de). This is especially useful in complex sentences to make it crystal clear exactly which noun the preposition applies to.

Give me the certificate, without which you cannot travel.
Dame el certificado, sin el cual no puedes viajar.
We read the new decree, according to which we must pay.
Leímos el nuevo decreto, según el cual hay que pagar.

Notice that when the preposition de (of/about) combines with the el in el cual, it forms the mandatory contraction del cual:

We must read the treaty about which they spoke.
Hay que leer el tratado del cual hablaron.