Q: What is a relative clause?
A1: One of Santa’s cousins, nieces, or nephews.
A2: A group of words to add more information to a sentence without starting a separate sentence that repeats some of the same
Separate Sentence Example:
We plan to repair the pump. The pump failed yesterday.
Combined Sentence with Relative Clause Example:
We plan to repair the pump that failed yesterday.
In the latter sentence, the relative clause is “that failed yesterday” and it starts with the relative pronoun “that,” which takes the place of the redundant “the pump.” Other common relative pronouns are: Who, Which, Whose, and Whom.
The pump will be repaired by a contractor who knows how to do it.
The contractor can do it in one hour, which is very fast.
He knows whose parts work best for these pumps.
This contractor is someone whom I once met on an airplane.
There are two kinds of relative clauses: Defining and Non-Defining. Some grammar gurus call them “Restrictive and Non-Restrictive,” and the AP Style Guide refers to them as “Essential and Non-Essential” clauses.
Anyway, the Defining / Essential / Restrictive relative clauses provide additional information that cannot be left out of the sentence without changing its meaning.
The Non-Defining / Non-Essential / Non-Restrictive relative clauses provide additional information in the sentence, but the
sentence can stand on its own without that clause.
Do you know a contractor who is good at fixing pumps? (won’t work without the clause)
The contractor, whom I met on an airplane, can fix pumps in one hour.
The contractor can fix pumps in one hour. (works just fine without the clause)
Here’s the Rule of Thumb for punctuating sentences with relative clauses:
Essential clauses do not need a comma; Non-Essential clauses need commas.
Technical writers who do not proofread their emails should be spanked.
(With no commas, this means only the ones who don’t proofread first should be spanked.)
Technical writers, who do not proofread their emails, should be spanked.
(With commas, this means all technical writers, who, by the way, happen to send emails without proofreading them first, should be spanked.)
So you see, commas can make a big difference in determining what information is essential and what isn’t in a sentence!