Indefinite Pronoun

The main role fulfilled by the indefinite pronoun is to allow the speaker to make a statement in generic terms, without necessarily defining the specific persons of whom the sentence is speaking.

The phrase, "One could say," is a good example of this: the pronoun doesn't specify who can say something; it merely indicates that some human being, somewhere, could say. It is important, though, to use the indefinite pronoun for a real purpose and not just degenerate into vagueness.

Understanding indefinite pronouns

The indefinite pronoun is a word that takes the place of a noun but without really specifying who or what it is taking the place of. 

In fact, in the phrase "one could say", the word "one" is an indefinite pronoun. It seems to be referring to a specific person; but at the same time, it is referring to no one in particular. Every indefinite pronoun is characterized by this general vagueness.  

Using indefinite pronouns in a sentence

Here is an example of the indefinite pronoun being used correctly in a sentence. 

"The boy asked his pastor what was meant by the old saying that 'many are called but only few are chosen.'"

In this sentence, the word "many" is an indefinite pronoun, and the word "few" is another. The words take the place of groups of people without necessarily specifying who belongs to those groups. 

Now, here is an example of the incorrect use of the indefinite pronoun. 

"Because of the dark, the girl was frightened: she could not see nobody."

This is incorrect usage of the indefinite pronoun because according to English rules regarding the use of the negative the last word should be "anybody". 

In case you are still a little confused, here are a couple general rules regarding the use of the indefinite pronoun. 

1. The main thing to think about is whether you are talking about a person or a thing, and then whether that group consists of no members, all possible members, some members, or at least one member. Each combination will produce a different common indefinite pronoun. 
2. Since the indefinite pronoun is in fact a pronoun, it implicitly takes the place of a common noun. For example, if you were to say, "Everybody likes me," what you are really saying is: "Every human being on this entire planet likes me." If you trace the sentence back in this way, it may become easier to choose the right indefinite pronoun for your specific situation. 

Comparing the term to other pronouns

In general, there are three main categories of the indefinite pronoun.

The negative refers to a situation where all members of the group are excluded ("nobody"); the universal refers to all members being included ("everybody").

The assertive says the group has at least one member ("somebody"); and the elective expresses uncertainty about whether the group has a member or does not ("anybody").

The quantifier indefinite pronoun category refers to words such as many, few, most, and several.

As with all pronouns, when you are using the indefinite pronoun, it is important that the flow of your thought makes the referent of the pronoun clear to the reader. For example, in the saying that many are called but few are chosen, the context makes it clear that we are talking here about people; in its extended form, the sentence would say: "Many people in the world are called, but only a few people in the world are chosen."

Of course, this would seem somewhat obnoxious to the reader insofar as he already gets the idea and does not need you to spell it out for him. The indefinite pronoun allows you to avoid such a situation.