Essential & Nonessential Information
Use commas in the middle of a sentence to set off words or phrases that are not essential to the meaning of the sentence.
The Boston Red Sox, however, have won the World Series only seven times.
This rule can be a little tricky because of some misinformation we may have received at some point in elementary school. Were you ever taught that the trick to determining whether or not you need commas around information in the middle of a sentence was to pull out that information and see if the sentence was still complete? If the sentence was still complete, then you would know you needed a comma around that extra information.
Well, that doesn’t always work so well.
The best tip is to think about how meaning would be affected if you pulled out the word or phrase. If the meaning is not really affected, the word or phrase is not essential and should be placed inside a set of commas.
Conversely, it’s important to remember that essential words or phrases should not be set off with commas.