Indefinite Pronouns

Indefinite Pronouns stand for some unspecified person(s), place(s) or thing(s).

Most indefinite pronouns are singular even though some of them (e.g., everyone, everybody) appear to have plural meanings.

Singular

another
anybody
anyone
anything

each
everybody
everyone
everything
either
neither

no one
nobody
nothing
one

somebody
someone
something

It is important to identify whether the pronoun is singular or plural
because singular indefinite pronouns take singular verbs or singular personal pronouns
while plural indefinite pronouns take plural verbs or plural personal pronouns.

Examples:
Plural

both, few, many, several

Examples:
Singular or Plural

any, all, more, most, none, some

The above indefinite pronouns may be singular or plural depending on the noun they refer to.

Examples:
Indefinite Adjectives

When used alone the words "all", "any", "both", "each", "every", "few", "many", "more", "most", "none", "several" and "some" function as indefinite pronouns.

But if these same words are used with nouns then they function like adjectives ... modifying the nouns that follow.
They answer the questions: How much? or How many? and are called "quantifiers".

Examples:

Pronoun: Both agreed that surgery was the only solution.
Adjective: Both doctors agreed that surgery was the only solution.

Pronoun: Many believe that aliens from outer space had landed on earth.
Adjective: Many people believe that aliens from outer space had landed on earth.