punctuation

 

prelude

For centuries, punctuation served as a rhetorical device, i.e., to guide the reader on when to stop or pause when reciting a text. In the late 17th century, the rhetorical uses of punctuation gradually came to be replaced with its logical functions in written prose, scientific literature, and mathematical expressions.

The guiding principle in using punctuation marks (as in much of the remainder of communication) is that, when the need for a mark is unclear, it should only be used if it reduces potential ambiguity. If text elements can be so logically arranged to make the meaning clear without punctuation, omit it. In other words—if in doubt, leave it out.

 

ON-THE-LINE PERIOD

Use the period . . .

. . . in decimal numbers.

Example:
The infant weighed 2.9 kg at birth.

. . . to close a complete sentence formatted as a list.

Example:
The study was carried out with 3 objectives in mind, i.e.,
        — to determine the efficacy of the compound,
        — to assess its influence on the patients’ quality of life, and
        — to identify its side effect profile.

. . . to abbreviate Latin phrases.

Examples:
e.g.,        i.e.,

Do not use the period . . .

. . . in or after abbreviations.

Examples:
Dr         PhD        USA

. . . after bullet points that are not sentences.

Example:
The objectives of the study were to:
        — determine the efficacy of the drug
        — assess its influence on the patients’ quality of life
        — evaluate its safety profile

 

COMMA

Use the comma . . .

. . . to set off an introductory word, phrase, or clause.

Examples:
Similarly, participants with the weakest grip strength were at greater risk of hospitalization.
To be sure, another study should be done.
While the cost of medical school in and of itself is certainly high, the true cost of becoming a doctor is in years and years of your life.

. . . to separate a nonrestrictive clause from the rest of the sentence.

Examples:
The program, which started in in 1995, teaches fifth-graders about the dangers of illegal drugs.

. . . to separate the elements of a series of more than 2 elements, with a comma preceding a closing ‘and’ or ‘or.’ This type of comma is called the Oxford, or serial, comma.

Examples:
He administered a cheap, effective, and readily available medication.
I bought a notebook, a printer, and an office chair.

Note:
Some style guides and writers prefer to omit the serial comma. However, routine use of the serial comma helps avoid ambiguity.

Examples:
For the long journey across the ocean, we brought along Jack, a singer and a cook.
For the long journey across the ocean, we brought along Jack, a singer, and a cook.

In the first sentence, it is unclear whether we asked 1 or 3 people to join us on our trip. The second sentence makes it unequivocally clear that we brought along 3 people. 

I love my dogs, Alice in Wonderland and Pooh Bear.
I love my dogs, Alice in Wonderland, and Pooh Bear.

The first sentence suggests that my dogs are called ‘Alice in Wonderland’ and ‘Pooh Bear’—when in fact they are called ‘Phoebe’ and ‘Honey’. Love the serial comma for the clarity it provides.

Biotechnology has applications in four major industrial areas, i.e., health care, crop production and agriculture, nonfood uses of crops and other agricultural products and environmental uses.
Biotechnology has applications in four major industrial areas, i.e., health care, crop production and agriculture, nonfood uses of crops and other agricultural products, and environmental uses.

Lack of the serial comma in the first sentence may cause the reader to wonder, if only briefly, which of the three items in the list—(1) nonfood uses of crops, (2) other agricultural products, (3) environmental uses—actually belong together. In the second sentence, the serial comma clearly maps out the syntactic structure and visually delineates each of the four areas announced in the first part of the sentence. Have I mentioned that I love the serial comma?

Following fermentation, centrifugation and sterile filtration ensure the removal of culture medium and most Escherichia coli cell debris.

While some recommend that the serial comma be used ‘as needed,’ ambiguity is avoided and ease of reading increased only if the serial comma is used routinely—as highlighted by the example above. Only if the reader can be sure that the serial comma is placed every time it’s required can he immediately be sure that the comma after ‘fermentation’ sets off an introductory phrase—rather than introducing a list of items.

 

 

HYPHEN

Use a hyphen . . .

. . . to form compound nouns or adjectives.

Examples:
light-year, cure-all, has-been
heavy-weight, well-established, short-lived

. . . to connect certain prefixes or suffixes to stem words.

Examples:
pre-Columbian [i.e., when connecting a prefix to a stem word that is is capitalized]
ex-wife, self-employed, balloon-like 

. . . in terms involving age.

Examples:
15-year-old girl
75-year-old patient

. . . in spelled-out fractions.

Example:
one-third of the population

Do not use a hyphen . . .

. . . to connect prefixes or suffixes in general. [British English often retains the hyphen in such cases.]

Examples:
metaanalysis, cooperate, coordination, preschooler

. . . as a connective in ranges of numbers, including confidence intervals.

Examples:
18 to 25 kg
CI, –1.21 to 1.25

 

EN-DASH

The length of the en-dash roughly corresponds with the width of the capital letter ‘N’. Its most common use in science writing is as the minus symbol.

Use an en-dash . . .

. . . as a minus sign (do not use a hyphen).

Example:
–4 °C

. . . in bibliographic references to link numbers representing the 1st and last pages.

Example:
Journal 1998;45:856–63.
. . . see pages 5–10.

. . . to link 2 words or phrases of equal rank.

Example:
gas–liquid chromatography

. . . as a coordinate connector in a term including hyphenated elements.

Example:
high–net-worth individual
avian-flu–related outbreaks

Do not use en en-dash . . . 

. . . with a minus symbol.

Examples:
–4 to 10 °C
–5 to –15 °C
weight changes of –2.5 to 3.6 kg

. . . in confidence intervals.

Examples:
CI, –1.21 to 1.25
. . . with a confidence interval of –1.21 to 1.25.

. . . with the word ‘from’.

Example:
. . . from page 5 to 10.

 

EM-DASH

The em-dash has lovingly been characterized as the most intuitive and versatile of punctuation marks—one that, once one has discovered its beauty, one will no longer want to do without.

The length of the em-dash roughly corresponds with the width of the capital letter ‘M’. Its length is equal to the size in points of the typeface, i.e., the em-dash in 10-point type is 10 points wide. An em-dash sets off amplifying or explanatory elements within a sentence—and can thus serve as an alternative to parentheses, commas, or a colon.

Use an em-dash . . .

. . . to indicate a parenthetic or sharp break in the sentence’s line of meaning.

Examples:
She spent 3 years on the West Coast—they may have been the happiest years in her life—before she moved to New York.
There has recently been an increase—though fiercely opposed by many—in alternative treatment practices.
My friends—my former friends, that is—ganged up on me.
He pays the bills—she has all the fun.
Where the heck is my—wait, what was I looking for?

. . . to add emphasis. Note how the em-dash alters the tone of sentences below.

Examples:
The influence of three impressionists—Monet, Sisley, and Degas—is obvious in her work.
The influence of three impressionists (Monet, Sisley, and Degas) is obvious in her work.

The medical community considers many cancers ‘cured’ when doctors cannot detect cancer 5 years after diagnosis—but recurrence after 5 years is still possible.
The medical community considers many cancers ‘cured’ when doctors cannot detect cancer 5 years after diagnosis, but recurrence after 5 years is still possible.

Taxes, emails, filing away all of my papers—it’s all done now, and I’ll take a rest.
Taxes, emails, filing away all of my papers: it’s all done now, and I’ll take a rest.

Survival statistics help doctors decide which treatments provide the most benefit—and to weigh the benefits against the risks.
Survival statistics help doctors decide which treatments provide the most benefit and to weigh the benefits against the risks.

 

QUOTIATION MARKS

American style uses double quotation marks for a primary quotation and single quotation marks for a quotation nested within a quotation. [British English uses the reverse order.]

Use double (primary) quotation marks . . .

. . . for a primary quotation.

Examples:
He considered the ecological effects an “utter disaster.”
He described the pandemic as fueling a “class struggle on a global scale,” and he presented numbers to support his claim.
“Be prepared to discuss not only your motivation for a career in medicine, but also any experiences that are relevant to your goal,” says one expert.
He shouted, “What a disaster,” and left.
Plato’s emphasis on the importance of moral education for the young raises the question, “Who ought to provide this education?” 

Use single (secondary) quotation marks . . .

. . . for a quotation nested within a quotation.

Example:
“Do you have any idea,” she asked, “what ‘chervil’ is?”

. . . to enclose a word that is not used functionally but is referred to as the word itself. The quotation marks should be used only at the first occurrence of the word. After that, it should be considered to be assimilated. Alternatively, such words may be italicized.

Examples:
The word ‘democracy’ has its origins in the Greek language.
The word democracy has its origins in the Greek language.

Note:
When introducing a foreign-language term, I generally italicize it and provide the English equivalent in single quotation marks.

Example:
The antipyretic and analgesic known in German by its INN Paracetamol is generally referred to as ‘acetaminophen’ in the USA.

. . . to alert readers to a term used ironically. These ‘scare quotes’ indicate that the enclosed word is not used in a way the writer would normally use it. The highlighted word or phrase is not necessarily a quote from another source. In speaking, scare quotes are generally expressed using ‘air quotes,’ by saying ‘quote unquote’ before or after the word or phrase, or by preceding it with the expression ‘so-called.’

Examples:
Most believers in ‘global warming’ believe that the burning of fossil fuels makes the earth warmer.
On a digital player, a ‘track’ is really just a file.
A ‘justice system’ that fails to deliver justice threatens the social order.

Position of quotation marks relative to other punctuation marks

American style positions commas and periods inside the closing quotation mark, even when they are not part of the quoted text. As the CBE Manual states, “this illogical practice appears to have arisen from American printers’ aesthetic distaste for the space beneath the closing quotation mark and the following period”—a distaste that I absolutely share. [In British English, the relationship between quotation marks and other marks of punctuation is strictly according to sense.]

Examples:
He considered the economic effects of the government’s measures a “true catastrophe.”
He described the pandemic as fueling a “class struggle on a global scale,” and he presented numbers to support his claim.

 

references

• Scientific Style and Format. The CBE Manual for Authors, Editors, and Publishers (6th edition)
• The Chicago Manual of Style (17th edition)
• The Oxford Guide to Style (2002 edition)