The use of commas with restrictive and nonrestrictive clauses has always been a source of great concern for the general population, so let’s clear up any misunderstandings that might still exist so that all, especially me, can move on with their lives.
Oftentimes, restrictive and nonrestrictive clauses are relative clauses. Relative
clauses use a relative pronoun (who, which, that, whom) and verb: who knows me, that like this food, whom he saw, which I watched yesterday.
A restrictive clause is essential to the meaning of the sentence and uses no
comma on either side of it. Were you to delete the restrictive clause, the meaning of the sentence would change:
My sister who lives in Nebraska was a musician in many bands. (If I had more than one sister, this helps the reader understand that I am discussing only the one who lives in Oregon, not any of the other sisters.)
On the other hand, a nonrestrictive clause is not essential to the sentence’s meaning, so you could lift out the clause enclosed by the commas—and the sentence’s meaning would be clear:
My sister, who lives in Nebraska, was a musician in many bands. I am discussing her profession, and the reader doesn’t know if I have one sister or several, but knowing that isn’t necessarily essential to the sentence’s meaning. What is contained in the commas is somewhat of an aside: “Oh yeah, and by the way, she lives in Nebraska.”
I hope you get lots of grammar presents over the holidays and during the year. And for this one, you’re welcome.
My English Quarters
Hallie Belt, M.A. and B.A., English