Understanding Commas
Rather than follow that mostly untrustworthy rule of “put a comma when you pause,”
here are the top three comma errors with more dependable rules to correct them.
Coordinating Conjunctions and Compound Sentences
Don’t be fooled; a comma does not always precede a coordinating conjunction (for, and, nor,
but, or, yet, so). Writers often want to use a comma when a coordinating conjunction connects
two elements of a sentence:
•
The hospital
receives
approximately 100 patients a day , but discharges only
half as many on a weekly basis.
•
Researchers were surprised to find the presence of bacteria , and other
contaminants in the test sample.
But a comma should ONLY be used when two or more independent clauses are joined
by a coordinating conjunction:
• Five participants in the study received the placebo, but only two reported feeling
any effects.
• The doctor discovered a unique strain of influenza, and the treatment had to be
altered.
Subordinating Conjunctions and Complex Sentences
When combining dependent clauses that begin with a subordinating conjunction (see
“The Basics of Syntax: Dependent Clauses” handout for more information), a comma is
required only if the dependent clause precedes the independent clause:
• Because the instructor changed the due date, the students spent their fall break
working on the assignment.
But if the dependent clause comes after the independent clause, no comma is
necessary:
• The students spent their fall break working on the assignment because the
instructor changed the due date.
Non-Restrictive Clauses
Additional information that is not imperative to a sentence’s main idea is called non-
restrictive information. Non-restrictive clauses must be set off with commas.
• Introductory/Transitional Elements
To create continuity, words, phrases and clauses can serve as transitions from
sentence to sentence and paragraph to paragraph, or they can introduce the
main idea of a sentence. A comma should follow the introductory/transitional
element to separate it from the independent clause.
Words:
First, all interviewees must bring a recent copy of their résumé.
Additionally, they should bring a portfolio of their work.
However, a headshot is not necessary and is strongly discouraged.
Phrases:
To clarify, this position will be filled according to the candidate’s merit rather
than his/her looks.
On the other hand, a winning smile has never disqualified a candidate.
Without a doubt, this company values a good attitude.
Waiting for her interview, Sarah re-read her résumé and rehearsed all of
her winning responses.
Flushed with anticipation, Sarah finally heard her name called.
• Adjectivals
Phrases that provide helpful but not imperative descriptive information about a
subject or object are called adjectivals. Similar to transitions, adjectivals can
appear at the beginning of a sentence, but they can also be moved around.
Because of their move-ability, adjectivals are almost always set off with commas.
For example:
The committee members, tenured faculty and leaders in their field, were
an intimidating group of people to face.
In this case, the adjectival is an appositive. “Tenured faculty and leaders in their
field” is a noun phrase that gives further detail about the subject: “the committee
members.” It interrupts the independent clause (“The committee members were
an intimidating group of people to face”) and thus is set off with commas. Notice
the adjectival can also be repositioned to precede the subject:
Tenured faculty and leaders in their field, the committee was an
intimidating group of people to face.
For further information on related concepts, please see the following handouts:
• The Basics of Syntax: Independent Clauses
• Transitions: Building Bridges Between Ideas
• Adjectivals
