Indefinite Pronouns
Like our 'stealth' singular nouns, many indefinite pronouns look like they should be plural but refer to only a singular subject and therefore require a singular verb form. These include the pronouns each, everyone, everybody, anyone, nobody, no one, nothing, everything, anybody, anyone, anything, someone, something, somebody, either, neither, other, and one.
In other words, you would say Everybody is going to the parade, not Everybody are going to the parade, or Someone leaves notes for me in my locker every morning, not Someone leave notes for me in my locker every morning. Why singular? Because while these indefinite pronouns may seem to refer to groups, they actually refer to individual actors - some (one) body or every (one) body or every (individual) thing.
I hope you don't find that too confusing, but if you do, you can always memorize these indefinite pronouns and remember that they call for a singular verb. You'll get the hang of it in no time.
Exceptions to Indefinite Pronouns
Though fewer in number, some indefinite pronouns always require a plural verb just as their brethren require a singular verb. These are few, many, both, others, and several. Remember the group nouns from earlier in the lesson? These indefinite pronouns have something in common with them in that they're singular nouns that are composed of more than one thing. The reason these always require a plural verb is that you can't break them down into their individual parts, nor can you have, say, six fews or a bushel of boths.
Here are a couple of examples of proper usage:
Many enjoy the daily clang of marching bands practicing in the street.
Few have ever tried to climb Certain Death Mountain.
Finally, five indefinite pronouns can be either plural or singular depending on context. These are most, any, none, some, and all, which you can remember by the mnemonic MANSA.
For example, Some of us have been enjoying this grammar lesson uses the plural form of the verb because the context says that you're referring to more than one member (i.e. 'some') of a group (that is, 'of us'). However, Some of the money is missing from the piggy bank requires a singular verb because 'some' is now describing a portion of a singular subject - that is, 'the money.'
Measurement
A similar rule applies when you're describing a percentage or part of something. For instance, the sentence Around 30 percent of football players are also proficient ballet dancers takes a plural verb ('are'), since in context, even though 'percent' looks singular, we're talking about a percent of a larger group of people (the football players), which is still plural. If the thing the percentage is referring to is singular, however, then the verb must be singular, as in Two-thirds of this pie has already been eaten or Three shots of vodka is three too many.