The question of whether to place a comma before the word "which" is one of the most common punctuation dilemmas in the English language. The short answer is that it depends entirely on the type of clause the word "which" is introducing. To master this rule, you must understand the difference between essential and non-essential information in a sentence.
When
When "which" introduces a non-essential clause, a comma is required before and after the word. This occurs when the
