Definitions and Distinctions

A pronoun is a word that represents and takes the place of a noun.

For example

In the following sentence:
The farmer ploughs the field; he reaps his wheat, and gathers it into his barn.
the pronouns he and his represent the noun farmer. The pronoun it represents the noun wheat.  

Pronouns take the place of a noun, not merely to be a substitute for it and thus avoid disagreeable repetitions, but to represent its important relationships.

• Sometimes a pronoun is used to avoid repetition as when a noun in the third person with its modifications would occur frequently in a sentence.
• Sometimes a pronoun is employed to avoid misapprehension or ambiguity as when the first or the second person becomes the object spoken of.
• Sometimes a pronoun is used to introduce an adjective expression to modify the noun as when by means of a relative pronoun and its clause, the meaning of a noun is restricted.
• Sometimes a pronoun is used to represent the noun as the subject of inquiry as when an interrogative pronoun is used in a question sentence.

The relationships that pronouns represent include the person relationship, that of the object spoken of to the speaker.
In this relation the object may be:

• the speaker
• the one spoken to
• the one spoken of

These are the first, the second, and the third person for personal pronouns. The pronouns I, you, (thou), he, she, and it, we, they  and some others refer to a speaker, those spoken to, or those spoken of.
A pronoum may refer to the object to some modifying circumstance.

For example

In the sentence:
A fortress which stands on a hill is a conspicuous object.
the pronoun which is used to denote the object, the fortress, and to join that reference to the circumstance of its position; that is, that it is conspicuous. Thus, the pronouns who, which, that, and what are called the relative pronouns.

    
The relationships that pronouns represent also include the object of an inquirer as in a question. Here, again, the object is represented by the pronoun, the name of the object being unknown, for the special purpose of making it a subject of inquiry. Hence, the interrogative pronouns are Who, Which, and What.

Personal pronouns of the third person and all the relative pronouns are employed when an object is supposed to be not only known, but to have been previously mentioned.
Personal pronouns of the first and the second person are used when the object is known but has not necessarily been previously mentioned.
Interrogative pronouns are used when the object is neither known nor previously mentioned.
    
The antecedent of a pronoun is the noun or substantive expression for which a pronoun stands.

For example

In the sentence:
The world in which they are placed, opens with all its wonders upon their eyes.
the antecedent of the relative pronoun which is the noun world.

The antecedent of a pronoun may be a word, a phrase or an entire proposition.

For example

In the sentence:
To believe the report, which is the thing you desire, would be offensive to one of the noblest of men.
the antecedent of the relative pronoun which is the phrase to believe the report.
In the sentence:
The servant opened the window, which was strictly forbidden.
the thing strictly forbidden that the relative pronoun which represents is the whole proposition the servant opened the window.

    
The term antecedent, however, usually means something more than the noun that the pronoun represents. It denotes the leading term of a relation, and implies a subsequent term. Hence, it is more especially used in the case of relative pronouns that are employed to show a relation between its antecedent noun and some following circumstances.
Personal pronouns bear no such syntactical relation to their antecedents.
The object represented by the personal pronouns of the first and the second person is assumed to be present, and, consequently, the antecedent noun is seldom given.
    
The antecedent noun for pronouns in the third person is usually expressed. Sometimes, however, a personal or an interrogative pronoun is employed without an antecedent, and so limited by a relative and its clause as to give to the whole the effect of a single name.

For example

He who sways the minds of men by his eloquence exerts the highest human power.
Who, that marks the fire still sparkling in each eye, but would deem their bosoms burned anew?

   
Sometimes the antecedent pronoun is omitted or is included in the relative.

For example

Who would be free, themselves must strike the blow.

Who steals my purse steals trash.
Shakespeare

The pronoun stands not merely for a noun, but for a noun as restricted by any modifying words.

For example

In the sentence:
We saw the little deformed boy who watched at the gate, and pitied him.
the antecedent of the pronoun him is the whole phrase the little deformed boy who watched at the gate.

  
The antecedent, as the term indicates, is something going before. Also, as an interrogative pronoun inquires for an object as yet unknown, the antecedent cannot be a preceding noun. The pronoun, therefore, must agree in person, and number, not necessarily with the noun in the answer, but with a noun which the speaker conceived to be the name of the object, however erroneous that thought might be, when the speaker uttered the question.

For example

What is there?

Note

The interrogative what normally refers to an animal or a thing. If the answer is a friend, that would normally refer to a person, and be referred with the interrogative pronoun who.