What is "which"? What is "that"?Versión en línea Dialogue por Yufei Jian Which I'm non-restrictive clauses which do not limit the words I modify. I simply add information that otherwise would not be provided.I am set off by commas because the information I provide is supplementary, not essential to the meaning of the sentence. That I'm restrictive clauses which modify, focus and limit. Because the information I supply is essential to the intended meaning of the sentence, I am not set off by commas. You Nice to meet you guys!