Commas, Colons, Semicolons and Dashes
Which Punctuation Mark Should I Use?
Knowing which punctuation to apply within sentences can be
confusing. But rules are important and made to be followed, especially in
academic writing. Putting a comma between two independent clauses will confuse
your readers and make your work frustrating to read. On the other hand, a
well-placed semi-colon can add nuance and subtlety to any kind of writing. Keep
the following rules in mind when choosing to use a comma (,), colon (:),
semicolon (;), or dash (—).
When to Use a Comma
Commas are the most frequently used (and abused) punctuation
mark in most kinds of writing. The reason for this is that they have so many
uses and so many rules—it can be hard to keep track of them all. Let’s take a
look at just a few of the comma’s crucial functions and discuss when to choose
a comma over another similar punctuation mark.
To list items or
short phrases:
I bought bread, cheese, and pickles at the grocery store.
To separate long independent clauses when conjunctions
connect them:
Astronomers have known about the positions of stars for
centuries, but they didn’t understand that the earth revolves around the sun.
After an introductory
phrase:
In preparation for the next convention, the representatives
studied up on the most important issues.
To separate a parenthetical phrase or interrupter:
All doctors, if they care about their patients, are
concerned with good office hygiene.
Common Comma Mistakes.
Comma splice. Do NOT use a comma to divide two independent
clauses without a conjunction.
Incorrect: Thousands of
protesters showed up on the streets, they were shouting and carrying large
posters.
Correct: Thousands of
protesters showed up on the streets; they were shouting and carrying large
posters.
Combining lengthy phrases. Using commas with compound
sentences or to separate clauses with other commas can cause confusion. Use a
semicolon.
Incorrect: Some useful
subjects are English, which is an international language, math, which is used
in all domains of sciences and social sciences, and philosophy, which underpins
many other areas of study.
Correct: Some useful
subjects are English, which is an international language; math, which is used
in all sciences and social sciences; and philosophy, which underpins many other
areas of study.
When to Use a Colon
A colon is used to make lists and tell the reader, “This is
what I mean.” The colon should not be used often in most kinds of writing
unless there are extensive lists involved. The rules of the colon are strict
but fairly easy to remember.
To introduce an item
or series of items:
Humans use five major senses: sight, hearing, smell, taste,
and touch.
To separate
independent clauses when the second clause/sentence illustrates, explains,
paraphrases, or expands on the first:
Martha realized that her worst fear was coming true: her son
was being sent to war.
(*The information after the colon explains Martha’s fear in
the form of an independent clause.)
To follow the
salutation in a business letter or more formal letter:
To the Central Valley Committee Chairman:
More Tips For Using
Colons
Do not capitalize the first word after the colon unless it
is a proper noun, is part of a quote, or is the first in a series of sentences:
Incorrect: I have three
desires: To eat, sleep, and work.
Correct: I have three
desires: to eat, sleep, and work.
When a quotation contains multiple sentences, many writers
prefer to introduce it with a colon rather than a comma:
In Chapter 3, the author explains his theory: “Dogs have
dreams, but they don’t dream as humans do. Their dreams reflect a primal desire
for pleasure, whereas humans are preoccupied with the ego and self-image. This
is equally true in wakefulness and sleep.”
A complete sentence after the colon is not necessary—a word
or phrase is fine.
There is one mantra that can sum up our position towards
climate change: urgent action.
Common Colon Mistakes
Separating two clauses that have equal rank or unrelated
information:
Incorrect: Sarah and her
friends loved spending time on the mountain: nature always held a special
meaning for them.
Correct: Sarah and her
friends loved spending time on the mountain; nature always held a special
meaning for them.
(*Use a period if the clauses are not at all related. Use a
semi-colon if the information in the second clause is somewhat related but does
not illustrate, explain, or paraphrase the first clause.)
Overusing the colon:
The colon is a powerful punctuation mark and should be used
sparingly. Think of it as a stop sign that calls readers’ attention and says,
“Hey! Pay attention to this. This is important.” If there are too many stop
signs on a street, you won’t be able to drive very smoothly or quickly. This is
the same effect colons can have upon readers.
Because colons are so attention-grabbing, they can clearly
indicate which information is important. For this reason, many authors use
colons to introduce their main argument or supporting evidence.
When to Use a
Semicolon
A semicolon is used to separate two ideas (two independent
clauses) that are closely related. They can also be used when listing complex
ideas or phrases that use commas within them.
Essentially, a semicolon is like a comma with more meaning or a colon
with more flexibility.
To join two or more ideas (parts) in a sentence when their
ideas are given equal position or rank:
The universe has always called to human beings; there could
be no more final frontier than space.
To join two independent clauses connected by conjunctive
adverbs or transitional phrases:
Sam thought David was inviting him to the picnic to enjoy a
nice day out; as it turned out, David was planning a surprise birthday party.
To present items in a list or series if there are commas
within the items, or if the items are relatively long and complex:
Our family members came all the way from Denver, Colorado;
Rochester, Minnesota; and even Paris, France.
To connect independent clauses joined by a coordinating
conjunction (if the clauses are already punctuated with commas) or if they are
lengthy.
My main research objective is to isolate the cause of the
disease, as well as to contribute to the existing literature; for this will
bring an end to starvation across the continent, create new study designs related
to epidemiology, and change the very paradigm of my research field.
Using a Semicolon
Instead of a Comma
Incorrect: The specimens were
treated properly, however, they were not stored properly.
Correct: The specimens
were treated properly; however, they were not stored properly.
*The conjunctive adverb “however” shows a connection between
the two independent clauses; do not use a comma to connect two independent
clauses without a coordinating conjunction (and, but, or, nor, etc.).
Incorrect: The sun is
wonderful: it produces light, which plants need to survive, it gives us warmth,
which is useful for most life, and it makes a sad day happier, which is
obviously a positive trait!
Correct: The sun is
wonderful: it produces light, which plants need to survive; it gives us warmth,
which is useful for most life; and it makes a sad day happier, which is
obviously a positive trait!
*Using only commas, it is unclear what items are being
listed exactly. Semicolons help divide listed items that each contain commas.
When to Use a Dash (or Dashes)
The dash (or, more specifically, the “em dash”) is perhaps
the most versatile of the punctuation marks. However, like the semicolon, it is
underutilized in most kinds of writing. It can function like a comma,
parentheses, or colon, but creating subtly different effects in each case.
Use Dashes in Place
of a Comma
Em dashes can be used in pairs to replaced commas when
writing a parenthetical or interruptive phrase. The dashes have a slightly more
emphatic feel, making the reader focus on this information that is set inside
the special marks.
Parenthetical phrase
with commas:
And so, when the baby was born in June, nearly two months
premature, the parents were happy but quite nervous, and they still had to buy
all of the baby supplies.
Parenthetical phrase
with dashes:
And so, when the baby was born in June—nearly two months
premature—the parents were happy but quite nervous, and they still had to buy
all of the baby supplies.
(*The dashes put emphasis on the fact that the baby was
premature, showing that it is an important detail in this sentence.)
Use Dashes in Place
of Parentheses
Put a pair of dashes in the same position that you would put
parentheses. Since they are less formal, fewer dashes than parentheses are
found in academic writing. However, they do cause more of an obvious
interruption and therefore more emphasis. They can also be used as a sort of
“meta” parentheses when the content between the dashes already contains
parentheses.
When dashes replace parentheses, the surrounded punctuation
is omitted:
Parentheses: After taking all of his final exams (including
seven essays and three multiple choice tests), David just wanted to sleep.
Dashes: After taking all of his final exams—including seven
essays and three multiple choice tests—David just wanted to sleep.
*The dashes are more visible and therefore interrupt the
flow of the sentence a bit more and draw attention to the content.
When used instead of parentheses at the end of a sentence,
only a single dash is used.
Parentheses: That coffee shop offers a selection of exotic
gourmet coffee (or at least that is how they describe it).
Single dash: That coffee shop offers a selection of exotic
gourmet coffee—or at least that is how they describe it.
*The dash seems to work especially well when placed at the end
of a sentence—it extends the sentence like an addendum.
Use a Dash in Place
of a Colon
Use an em dash instead of a colon when you want to emphasize
the conclusion of your sentence without giving it all of the connotations that
a colon brings. A dash can add “extra” information and is more flexible in this
way. It is also less formal than a colon.
Colon: The executives finally decided what they would do
with the company: sell it at a loss.
Single Dash: The executives finally decided what they would
do with the company—sell it at a loss.
Colon: Let’s go where we went last year: Disneyland!
Single Dash: Let’s go where we went last year—Disneyland!
*Using the dash in this way conveys a sense of anticipation
(or of inevitability) and can add an almost editorial feel to the writing.
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