English Grammar : article, syntax, verbs conjugation, English spelling

Because pronouns do not follow the standard rules for forming possessives and contractions, telling the difference between a possessive pronoun and a pronoun contraction can be difficult.

The inflections of most English words are not affected by case. That is, most words are spelled and pronounced the same way no matter where they appear in a sentence. Pronouns, however, are modified according to whether they are being used in the first, second or third person, and whether they are being used as the subject or object of the verb. Consider, for example, the personal pronoun in the first, second, and third person singular nominative case:

First person: I
Second person: you
Third person: he/she
In the objective case (the object of the verb) the pronouns are quite different:

First person: me
Second person: you
Third person: him/her
When forming possessives, the differences are similarly dramatic:

First person: my
Second person: your
Third person: his/her
The general rule for forming possessives from nouns is to add “'s” to the end of the word. Among pronouns, this rule only applies to “it.” However, the contraction of a noun and “is” is formed by the same rule. To avoid confusion (though the result can be just as confusing), the apostrophe ( ' ) is removed from the possessive of “it.”

Possessive: “it” its
Contraction: “it is” it's
The second person possessive pronoun “your” presents a similar problem. The contraction of “you” + “are” is “you're,” according to the general rule. The possessive form of “you” is “your,” which is spelled almost the same and is pronounced exactly the same in most dialects. This causes a good deal of confusion even for native English speakers:

Possessive: “you” your
Contraction: “you are” you're
The pronoun “they” also has several homonyms (words that sound the same but are spelled differently and have different meanings):

Possessive: “they” their
Contraction: “they are” they're
Adberve of place: there