Commas that separate Non-restrictive Clauses
Subordinate
clauses can be restrictive (they are vital to the meaning of the main clause)
or non-restrictive (they add some new information). Restrictive clauses do not
require commas; non-restrictive clauses do.
Restrictive
People who
like sports are our best customers.
Do not go
until you have read all the directions.
It was a
report which he desperately needed.
Non-Restrictive
Boston,
which is the site of the famous Tea Party, is a very old city.
He gave the
money to Leonard Sedder, who is my father-in-law.
You are
all invited to come, although the weather might be fairly cool.
Adapted from Stevens Institute of Technology
