grammar.articles.contractions-al-del
Al and del: the only two contractions
A + el = al, de + el = del — mandatory: voy al banco, vengo del trabajo. Never with la/los/las or with proper names containing El.
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Explication
Spanish has exactly two contractions, and both are obligatory. A + el merges into al, and de + el merges into del: voy al banco, vengo del trabajo, la oficina del jefe. Writing them out (*a el banco, *de el trabajo) is always wrong.
They happen only with the masculine singular article el. The other articles never contract: a la playa, de los clientes, a las nueve, de las afueras.
One exception: no contraction when El is part of a proper name, because there El is a capitalized word, not the article — el equipo de El Alto, vengo de El Salvador. (And a + él, the pronoun with an accent, never contracts either: se lo di a él.)
Exemples
We're going downtown.
Région: global
He's the owner of the building.
Région: global
I left work and went straight to the gym.