Pronouns usually refer to other words, called their antecedents because they (should) come before the pronoun. A pronoun's antecedent may be either a noun or another pronoun, but in either case, it must be clear what the antecedent is. Consider this example:
Micheline told Ruth that she would take Jerry to the barn dance.
It is not clear whether the pronoun "she" in this sentence refers to Ruth or Micheline. Unless pronouns refer unmistakably to distinct, close, and single antecedents, the reader will never be sure who's going to the square dance with whom.
A pronoun should have only one possible antecedent
If there is more than one possible antecedent for a personal pronoun in a sentence, make sure that the pronoun refers only to one of them:
WRONG Jerry found a gun in the trousers which he wore.
"Which he wore" could modify "trousers" or "gun."
WRONG Jerry called Steve twelve times while he was in Reno.
The pronoun "he" could refer either to "Jerry" or to "Steve."
A pronoun should not refer to an implied idea
Make sure that the pronoun refers to a specific rather than to an implicit antecedent: When you leave the antecedent implied instead of stating it explicitly, the reader has to try to guess your sentence's meaning:
WRONG John put a bullet in his gun and shot it.
The pronoun "it" can refer either to the noun "gun" or to the implied object of the verb "shot."
WRONG If I told you had a beautiful body would you hold it against me?
The pronoun "it" can refer to the noun "body" or to the entire statement.
WRONG The craftspersons' union reached an agreement on Ruth's penalty, but it took time.
The pronoun "it" can refer to the noun "union" or to the implied process of decision making.
A pronoun should not refer to adjectives or possessive nouns
You should not use adjectives, or nouns or pronouns in the possessive case, as antecedents. Although they may imply a noun, reference to them will be ambiguous:
In Ruth's apology she told Jerry she'd loved him for years.
In this case, the pronoun "she" seems to refer to the noun phrase "Ruth's apology," though it was probably meant to refer to possessive noun "Ruth's."
Jerry wore those blasted green knickers; it was his favourite colour.
In this example, the pronoun "it" seems to refer to the noun "knickers," though it was probably meant to refer to the adjective "green."
A pronoun should not refer to a title
When you start your paper, do not write as if the title itself were part of the body of the paper. Often, the title will appear on a separate page, and your opening will be confusing. Imagine, for example, a paper entitled "How to Sew Green Knickers": you should not begin the first paragraph with a sentence like
This is not as easy as it looks.
The writer probably wanted the pronoun "this" to refer to the idea of sewing knickers, but since the idea is not in the body of the paper itself, the reference will not make sense.
Use "it," "they," and "you" carefully
In conversation people often use expressions such as "It says in this book that ..." and "In my home town they say that ...". These constructions are useful for information conversation because they allow you to present ideas casually, without supporting evidence; for academic writing, however, these constructions are either too imprecise or too wordy:
WRONG In Chapter four of my autobiography it says that I was born out of wedlock.
In Chapter four, what says that the speaker was born out of wedlock?
WRONG In the restaurant they gave me someone else's linguini.
Who gave the speaker someone else's linguini?
It would be better to rewrite these two sentences as follow:
RIGHT Chapter four of my autobiography states that I was born out of wedlock.
RIGHT In the restaurant, the server gave me someone else's linguini.
In these revised sentences, there is no doubt about who is doing what.
The same basic rule applies to the pronoun "you." In informal conversation and in instructional writing (like HyperGrammar), English speakers often use the pronoun to mean something like "a hypothetical person" or "people in general"; academic writing, however, needs to be more precise, and you should use "you" only when you want to address the reader directly (as I am doing here). Consider this example:
WRONG In the fourteenth century, you had to struggle to survive.
In this case, "you" obviously does not refer to the reader, since the reader was not alive during the seventeenth century. It would be better to rewrite the sentence so that it expresses your idea more precisely; for example
RIGHT In the fourteenth century, people had to struggle to survive.
Or even better yet,
RIGHT In the fourteenth century, English peasant farmers had to struggle to survive.
Use "it" consistently within a sentence
There are three common uses of the pronoun "it":
As an idiom
"It is snowing";
To postpone the subject
"It is untrue that a rhinoceros can run faster than my tights"; and
As a personal pronoun
"I wanted a rhinoceros for my birthday, but did not get it."
You may use all of these in academic writing, but to avoid awkwardness, you should not use more than one within a single sentence:
WRONG When it is my birthday, I hope to receive a rhinoceros, and I will walk it often.
It would be better to eliminate the first (idiomatic) "it":
On my birthday, I hope to receive a rhinoceros, and I will walk it often.
Use "who," "which," and "that" carefully
Historically, writers, editors, and publishers have had difficulty establishing a clear guidelines for using the relative pronouns "who," "which," and "that," in formal writing, but over the last fifty years or so they have come a loose standard. According to this standard, the pronoun "who" usually refers to people, but may also refer to animals that have names:
My mother, who gave me the rhino, must love me very much. My rhino, whom I call Spike, wanders at will through the house.
The pronoun "which" refers to animals and things:
The rhino, which is a much maligned and misunderstood animal, is really quite affectionate. Its horn is a matt of hair which is sort of stuck to its snout.
Finally, the pronoun "that" refers to animals and things and occasionally to persons when they are collective or anonymous:
The rhino that hid behind the television was missing for days.
Rhinos that like to swim cause both plumbing and enamelling problems for their owners.
The answer that everyone missed was "Etruscan."