Assertive Indefinite Pronouns and Determiners

roughly or around a stated number

There were some 50 people at the event.

a person who is not mentioned by name

Someone left their umbrella in the hallway.

a person whose identity is not specified or known

Somebody left their keys on the table.

used to mention a thing that is not known or named

I need to buy something for dinner tonight.

feeling completely sure about something and showing that you believe it

Being certain of her feelings, she decided to confess her love.