Whether an indefinite subject is singular or plural depends on whether the indefinite noun has a singular or plural meaning on its own or based on the rest of the sentence.
Scenario 1: Indefinite subject with singular meaning on its own
Example: Each of the fossils in the Petrified Forest National Park tells a story.
Even though there is more than one fossil, the word “each” is always singular. Many indefinite subjects are always singular. Examples include another, anyone, anything, each, everybody, everything, neither, nobody, one, other, and something.
Scenario 2: Indefinite subject with singular meaning based on the rest of the sentence
Example: All of Arizona was once located in a tropical region.
Since “Arizona” is singular, “all” is singular. Some indefinite subjects can be singular or plural. Examples include all, any, more, most, none, some, and such.
Scenario 3: Indefinite subject with plural meaning based on the rest of the sentence
Example: All the petrified trees in the Petrified Forest National Park are millions of years old.
Since “trees” is plural, “all” is plural.
Scenario 4: Indefinite subject with plural meaning on its own
Example: Both scrubland and rock formations are common in desert settings.
Some indefinite subjects are always plural. Examples include both, few, fewer, many, others, several, and they.
