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Who v Which v That

Rule 1	Who refers to people. That and which refer to groups or things.
	Examples	Anya is the one who* rescued the bird*
		Lokua is on the team that* won first place*
		She belongs to an organization that specializes in saving endangered species.

Rule 2	That introduces essential clauses while which introduces nonessential clauses.
	Examples	I do not trust editorials that* claim racial differences in intelligence.*
		We would not know which editorials were being discussed without the that clause.
		The editorial claiming racial differences in intelligence, which* appeared in the Sunday newspaper, upset me.*
		The editorial is already identified. Therefore, which begins a nonessential clause.
	NOTE	Essential clauses do not have commas surrounding them while nonessential clauses do contain commas.

Rule 3	If this, that, these, or those has already introduced an essential clause, use which to introduce the next clause, whether it is essential or nonessential.
	Examples	That is a decision which you must live with for the rest of your life.
	Examples	Those ideas, which we've discussed thoroughly enough, do not need to be addressed again.
	NOTE	Often, you can streamline your sentence by leaving out which.
	Example	Those ideas, which we have discussed thoroughly, do not need to be addressed again.
	Better	The ideas we have discussed thoroughly do not need to be addressed again.
	Example	That is a decision which you must live with for the rest of your life.
	Better	That is a decision you must live with for the rest of your life. or You must live with that* decision for the rest of your life.*