When a sentence includes an extra phrase beginning with the word which is comma needed?

You're asking about nonrestrictive clauses, which are phrases that add extra information to a sentence but aren't essential to its meaning. They are often introduced by the word "which" and are always set off by commas.

Here's a breakdown:

Restrictive clauses: These are essential to the meaning of the sentence and are not set off by commas. They tell us which specific item we are talking about.

* Example: "The car that is red is mine." (This tells us which car is yours, the red one)

Nonrestrictive clauses: These provide additional information and are not essential to the meaning of the sentence. They are set off by commas because they can be removed without changing the sentence's core meaning.

* Example: "The car, which is red, is mine." (We know which car is yours, but the red color is extra information)

Here are some rules to remember:

* Use commas around "which" when it introduces a nonrestrictive clause.

* Don't use commas around "which" when it introduces a restrictive clause.

Let's look at some examples:

With commas:

* "The book, which I bought at the bookstore, is very interesting."

* "The dog, which is a golden retriever, is very friendly."

* "The movie, which was released last week, is getting great reviews."

Without commas:

* "The book that I bought at the bookstore is very interesting."

* "The dog that is a golden retriever is very friendly."

* "The movie that was released last week is getting great reviews."

Remember: If you can remove the phrase beginning with "which" without changing the meaning of the sentence, you need commas!