Rule 6: Interrupters & Parentheticals
Rule: Set off interrupting phrases and parenthetical expressions with commas.
As I was saying To tell the truth mind you in my opinion on the other hand without a doubt I hope
consequently I presume I suppose if you ask me for instance nevertheless
of course for example on the contrary I believe
Example: Jerry, I believe, is a genius in math. (use commas because "I believe" interrupts the sentence)
I believe Jerry is a genius in math. (no commas because there is no interruption)
Example: Mrs. Jones, who works at Ogles, helped me find spinach and pickles.
The lady who works at Ogles helped me find spinach and pickles. (no comma because there is no interruption)