The word _I_ in the first sentence, the word _thou_ in the second, and the
word _he_ in the third have each a different use. _I_, _thou_, and _he_ are
personal pronouns, and, as you have learned, distinguish _person_ by their
_form_. _I_, denoting the speaker, is in the +First Person+; _thou_,
denoting the one spoken to, is in the +Second Person+; and _he_, denoting
the one spoken of, is in the +Third Person+.

_Personal pronouns_ and _verbs_ are the only words that distinguish person
by their form.

_The bear killed the man_. _The man killed the bear_. _The bear's grease
was made into hair oil_. In the first sentence, the bear is represented as
_performing_ an action; in the second, as _receiving_ an action; in the
third, as _possessing_ something. So the word _bear_ in these sentences has
three different uses. These uses of nouns are called +Cases+. The use of a
noun as subject is called the +Nominative Case+; its use as object is
called the +Objective Case+; and its use to denote possession is called the
+Possessive Case+.

The _possessive_ is the only case of nouns that is indicated by a change in
_form_.

A noun or pronoun used as an _attribute_ complement is in the _nominative
case_. A noun or pronoun following a preposition as the principal word of a
phrase is in the _objective case_. _I_ and _he_ are _nominative_ forms.
_Me_ and _him_ are _objective_ forms.

The following sentences are therefore incorrect: It is _me_; It is _him_;
_Me_ gave the pen to _he_.