When the relative pronoun is the object of a preposition, the definite article is added to que, and this agrees for number and gender, giving us el que, la que, los que, las que and the neuter lo que. Note that in English there are two options: the preposition can go to the end of the sentence, or it can go right before the relative pronoun "which" or "whom".
- Ella es la persona a la que le di el dinero = "She is the person I gave the money to" / "She is the person to whom I gave the money"
- Es el camino por el que caminabais = "It is the path you were all walking along" / "It is the path along which you were all walking"
In some people's style of speaking, this definite article may be omitted after a, con and de, particularly when the antecedent is abstract or neuter:
- La aspereza con que la trataba = "The harshness with which he treated her"
- No tengo nada en que creer = "I have not anything to believe in" / "I have nothing in which to believe"
After en, the article tends to be omitted if precise spatial location is not intended.
- Lo hiciste de la misma forma en que lo hizo él = "You did it the same way he did it" (note also how "in" with the word forma is translated as de when used directly, but then changes to en when used with the relative pronoun)
- La casa en que vivo = "The house in which I live" (as opposed to the following:)
- La casa en la que estoy encerrado = "The house inside which I am trapped"