that vs. which

Use “that” and “which” in referring to inanimate objects and to animals without a name. The difference between these words has to do with essential vs. non-essential clauses. If you can drop the clause and not lose the meaning of the sentence, use which; otherwise, use that. In other words: Use that for essential clauses, important to the meaning of a sentence, and without commas: I remember the day that we met. Use which for nonessential clauses, where the pronoun is less necessary, and use commas: I remember the day that we met your friends for coffee, which was delicious.