Usage Note
Alguien is invariable and always refers to people ('someone, somebody'), contrasting with algo for things ('something'). It triggers masculine singular agreement on adjectives: alguien inteligente (not alguiena). In negative contexts nadie replaces it: No vino nadie (not No vino alguien).
Examples
"Alguien dejó la puerta abierta."
Natural Translation
Someone left the door open.
Related Words
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