Rule 1. Who
refers to people. That and which refer to
groups or things.
Examples Glen is the one who
rescued the bird.
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 like editorials that
argue for racial differences in intelligence.
We would not know which editorials were being
discussed without the that clause.
The editorial arguing for 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 that
has already been used in the sentence, use which
to introduce the essential clause that follows.
Example That is a decision which
you must live with for the rest of your life.
Rule 4. If the
essential clause starts with this, that, these, or
those, use which to connect.
Example Those ideas which
were discussed on Tuesday will be put in the minutes
of the meeting.
Even better The ideas discussed on Tuesday will be .
. .