- The judge’s comment, which was very nasty and uncalled for, destroyed the contestant’s confidence.
- But the next judge made a good comment that helped the contestant move to the next round.
That tells us essential information is coming up, information that further defines an item to a specific category or definition. In our example, that shows the importance of the comment made by the judge. It’s not just a comment, it’s the kind of comment that helps contestants move to the next round. Notice the lack of commas. Restrictive clauses do not use commas.
Which, however, tells us nonessential information is coming, information that adds to or comments on an item that’s already identified. It does not further classify the item. In our example, which gives us additional information about the comment but could be taken out of the sentence without harm to the sentence. Notice the commas. Nonrestrictive clauses use commas.
So here’s our rule of thumb:
Determine the type of information—if it’s essential information, use that without any commas; if it’s nonessential, use which with commas. For more information, refer to The Chicago Manual of Style or a usage dictionary.