A pronoun is a word that refers back to a noun, or takes the place of a noun. These simple words can cause readers great confusion, even when technically used properly.
Agreement in Number
One of the primary problems with using pronouns is agreement. If a pronoun takes the place of a singular noun, then it too must be singular. For example:
It is often easier to make generalized nouns plural than deal with the clunky phrase "he or she"; for more information, see our page on guidelines for nonsexist usage.
Also remember that the words "everybody," "anybody," "anyone," "each," "neither," "nobody," and "someone" are all singular and thus take singular pronouns.
Agreement in Person
If you are writing in one person, e.g. third (he, she, it, they, etc.), then do not switch to another person, e.g. second (you).
Consider this sentence:
The reader cannot tell whether "It" at the beginning of the second sentence refers to the treaty or to the peaceful way of setting disputes. Using "This was" instead of "it was" wouldn't help the reader very much. Consider these revisions of the second sentence:
Both of these revisions provide much-needed clarity for the reader. As a part of the editing process, it can be useful to comb through your paper, either by hand or using the search function on your computer, and locate all vague pronouns such as "this," "that," "it," etc. Try to replace as many of these pronouns as possible to convey your message clearly.