That and Which: Which Should I Use?
Ever since I started working as a copy editor, I’ve come across certain issues more often than others. One of the more common ones is swapping “that” and “which.” What makes this fun (depending on your definition) is that the rules are different between American and British English. Here, I’m focusing on American English.
To keep it simple, use “that” for information necessary to the sentence, and use “which” for information that can be removed. Notice that changing the term in the following sentence actually alters the meaning:
The company’s office that has two lunch rooms is located in Cincinnati.
This indicates that the company has multiple offices, but the one with two lunch rooms is in Cincinnati.
The company’s office, which has two lunch rooms, is located in Cincinnati.
This indicates that the company’s sole office is in Cincinnati, and super cool fact, it has two lunch rooms (jealous?)
“Which has two lunch rooms” can be removed from the second sentence and the overall statement will still be true: the office is located in Cincinnati. If we removed “that has two lunch rooms” from the first sentence, we wouldn’t know that this company actually has multiple offices, one of which happens to be in Cincinnati. Confused yet?
Here’s an example that’s more relatable to the medical field. Which term should we use?
Eosinophilic esophagitis is a noninfectious, allergic inflammation of the esophagus resulting in symptoms of esophageal dysfunction such as dysphagia, food impaction, and epigastric or chest pain which/that does not respond to proton pump inhibitors.
Here, leaving “which” indicates that the information that follows can be removed from the sentence without changing its meaning, but is this true?
…resulting in symptoms of esophageal dysfunction such as dysphagia, food impaction, and epigastric or chest pain.
…resulting in symptoms of esophageal dysfunction such as dysphagia, food impaction, and epigastric or chest pain that does not respond to proton pump inhibitors.
Using “that” specifies exactly what type of epigastric or chest pain we’re talking about: the kind that doesn’t respond to proton pump inhibitors.
As an extra tip, these removable parts of a sentence beginning with “which” are typically set off with commas. Notice the commas in the example that includes “which has two lunch rooms” —they help indicate that this information does not affect the sentence’s meaning. Patricia T. O’Conner includes a useful memory aid in her grammar book Woe Is I:
Commas, which cut out the fat, go with which, never with that.
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