Alguien dejó su libro en la mesa.

the book

Breakdown of Alguien dejó su libro en la mesa.

• en: on
• la mesa: the table
• su: their

Questions & Answers about Alguien dejó su libro en la mesa.

Why does alguien need a third-person singular verb like dejó?

In Spanish, alguien is treated as a singular pronoun, so the verb must agree with the third-person singular (él/ella/usted). That’s why we use dejó instead of something like dejaron.

Why is su used here instead of su libro de él or su libro de ella?

In Spanish, the possessive adjective su can mean his, her, your (formal), or their—all of these senses are context-dependent. You don’t need to clarify whether it’s de él or de ella unless it’s ambiguous and you really want to emphasize whose book it is.

Does su ever mean your in this sentence?

It can, if the context requires it. For example, if you’re addressing someone formally and implying someone (you) left your book on the table. However, without further context, it most directly reads as someone left his/her/their book on the table.

Why do we say en la mesa instead of just en mesa?

In Spanish, you typically use the definite article (la) before nouns to refer to a specific place or thing, especially for locations like la mesa (the table). Omitting it would sound unnatural to Spanish speakers.