Editing Tip: 'That' vs. 'Which'

In scholarly writing, the words ‘that' and ‘which' are frequently used to introduce additional information about important items. Here is some information about the implications of each word and when to use one or the other.

Using 'that'

Many sentences mention a specific person, object, or concept and then follow up with information designed to provide further clarification or description. At times, this additional information is essential to the understanding of the sentence, and at other times, the information is simply provided for reference. When the information is essential, it is considered a restrictive element, and the word ‘that' should be used to introduce it. (Please note that a comma is never placed before the word ‘that.') For example:

• The car that is parked next to mine has a flame painted on the hood. (The location of the car is a necessary piece of information to specifically identify the car being discussed.)
• The cells that were transfected glowed green. (That is, only transfected cells glowed green; presumably other cells were present, but those cells did not glow if they had not been transfected.)

Using 'which'

When the information is not essential and only provides more context or an interesting fact, it is considered nonrestrictive. Such information is introduced with the word ‘which,' as in the following examples (please note that a comma is always used before the word ‘which'):

• Uruguay, which won the first FIFA world cup, will play against Venezuela later this summer. (The historical fact about Uruguay is not essential to understand the rest of the sentence.)
• Vibrio cholerae, which causes the deadly diarrheal disease cholera, is endemic to many tropical regions. (The additional information about the bacterium is not necessary to understand where it can be found.)

We hope that these examples have provided some insight into how to use these two important words in your writing! Please email us with any questions or comments.