Pronouns behave in some ways like nouns and can sometimes replace them in a sentence. For this reason, pronouns are often treated as a subclass of nouns and there are some good reasons for doing this, but they are – in some important ways – different from nouns.
A major difference between pronouns and nouns generally is that pronouns do not take the or a/an before them. Further, pronouns do not take adjectives before them, except in very restricted constructions involving some indefinite pronouns (a little something, a certain someone).
While the class of nouns as a whole is an open class, the class of pronouns is a closed class. In other words, while the English language is constantly having new nouns added to it, we do not often see new pronouns appearing. A possible candidate is themself. Some pronouns have been lost, e.g. thee, thy, thou.
English has a few peculiarities regarding pronouns. For example, we may or may not include the addressee(s) or other people, and you plural may or may not include someone other than the addressee(s). For example, iif someone says ‘We’re all in this together’, we could refer to all of us, or a smaller group of people.
Likewise, you has been both a singular and plural form since the 17th century. Before that time, you was the plural form and thou was the singular. The reasons for the disappearance of thou are interesting, but since it disappeared, many regional varieties of English have developed their own means of expressing the second person plural, including yous, you all, y'all, yinz, and even you guys.
As well as the personal pronouns, there are other types of pronoun, which we offer examples of here.
The categories above do not show distinctions between genders, or between first, second and third person - those distinctions apply only to personal pronouns.
Many of the word forms listed above can also belong to another word class – the class of determiners. When a noun follows them (e.g. This car is new) they are demonstrative pronouns and also determiners.