That, which, who (grammar final)

Nonessential phrase

Can be removed without changing the meaning of the sentence. Not critical to understanding the sentence. Uses which and who with a comma.

Essential phrase

Critical to interpreting the sentence. Uses that and who without a comma.

Essential phrase (summary)

Inanimate object: That Person or named animal: Who Comma: No

Nonessential phrase (summary)

Inanimate object: Which Person or named animal: Who Comma: Yes

Who

Used instead of either that or which when it refers to a person or a names animal. That or which is used with inanimate objects or unnamed animals.

That

Used with essential clauses and never has a comma. Ex: Corgi is the breed that I like best.

Which

Used with nonessential clauses and always has a comma Ex: The corgi, which is my favorite breed, is at home in the palace.