Four pronouns cause writers more trouble than all the others do. They are
The most frequent mistake that writers make when using these pronouns is trying to make them stand for entire ideas or phrases instead of individual people, places, or things. The second-most-frequent mistake is not taking care to see that they refer to only one person, place, or thing at a time.
Consider the following paragraph, taking special notice of the pronouns in bold type:
Center City nestles in a valley cut by a lazy river, which winds toward the west. This means that the city is divided in two. In winter, snowfalls can be heavy, and it makes travel difficult in the valley. The population is a unique blend of ethnic groups. That gives Center City a rich culture.
Well consider the problems with each of these pronouns in turn.
First, the reader cant be sure whether which refers to the valley or the river or both. To make the reference clear, the writer should rephrase the sentence:
Center City nestles in a valley cut by a lazy river that winds toward the west.
Now the reader knows that the river winds toward the west.
Second, the reader cannot tell what this refers to because it does not refer to any word that came before it. Instead, the writer wants it to refer to a concept in the first sentence. That concept is the fact that Center City is cut by the river. To make the reference clear, the writer should spell it out by stating the concept:
The way the river runs through Center City means that the city is divided in two.
Third, the reader cannot be sure what it refers to. The writer was trying to avoid repeating snow but confused the reader by doing so. The writer should either go ahead and repeat snow or find a clear way to avoid repeating it:
In winter, snowfalls can be heavy, and all that snow makes travel difficult in the valley.
Finally, the writer has made the same mistake with that as with this earlier. The writer uses that to refer to an entire concept, not to a word. The concept should be named:
The population is a unique blend of ethnic groups. That blend gives Center City a rich culture.
What is wrong with using a pronoun to refer to the entire idea expressed in a sentence?