Style Guide: Grammar and Usage

Use this page as guide to common grammar style questions.

Cumberland Project Aerial photograph in the early morning of cliffs at sunrise along a mountain spine. N36°27.685' W84°01.171' 5/28/19 © Cameron Davidson

We've all learned different rules for grammar and style over our schooling and various work experiences. Maintaining a level of consistency strengthens the branding and authority of our site and our organization.

While some of these rules are straightforward, many rely on judgment calls. Take Oxford (or serial) commas, a highly debated subject. In general, we rely on the Associated Press (AP) style rules. 

If you have a grammar rule that you think should be added, please reach out via the Digital Request Form and choose "Digital Learning."

General Grammar

& (ampersand) 

Use only if part of a company name. Should never replace and in common text, except for some accepted abbreviations.

Titles of Compositions
Italicize titles of publications and compositions (books, movies, songs, television programs, lectures, works of art, scientific journals, etc.). Put quotes around titles of short works (poems, stories, articles) and divisions of longer works (chapters, sections).

Indicated within parenthesis, in roman. Use small caps to show stress. May be preceded with the word pronounced in roman inside the parenthesis:

Maurice River (MOR-ris)
Xia (pronounced shah)

Use a slash, rather than a hyphen, for constructions such as and/or, either/or, over/under, red state/blue state, etc. No space on either side of the slash.

Oxford commas
In most simple series, do not use a comma before the conjunction: The flag is red, white and blue. They are standing almost at the spot where the borders of Virginia, Tennessee and Kentucky meet.

However, if omitting a final comma in a simple series would make the meaning unclear, include it. The governor convened his most trusted advisers, economist Olivia Schneider and polling expert Carlton Torres. (If Schneider and Torres are his most trusted advisers, don’t use the final comma.) The governor convened his most trusted advisers, economist Olivia Schneider, and polling expert Carlton Torres. (If the governor is convening unidentified advisers plus Schneider and Torres, the final comma is needed.)

TNC example: Panthers are impacted by genetic issues, reduction in available prey, and intraspecies aggression. (Without a comma, the reader might think there is a reduction in intraspecies aggression.)

If an integral element of the series requires a conjunction, put a comma before the concluding conjunction: I had orange juice, toast, and ham and eggs for breakfast.


Geographic Names
Follow AP style in general (Mississippi River, the river; Philippines Islands, the islands) but note the following exceptions, per Words into Type: the Gulf (Gulf of Mexico), the Falls (Niagara Falls), the Canal (Panama Canal), the Street (Wall Street).

Popular and legendary names of places are capitalized and not enclosed in quotation marks (Chicago), e.g., Eastern Shore (of Chesapeake Bay), Lake District, the Piedmont

Headline Capitalization / Title Case
Capitalize first and last words, proper nouns, important words and all prepositions longer than three letters. Also, the first word after a colon is always uppercase in headlines.

Hyphens, em dashes and en dashes

Not all dashes are equal

-           Hyphen (use as joiners between words)

–          En dash (don’t use them)

—        Em dash (use to signal an abrupt change in a sentence)


If the sheer number of hyphens in a phrase, or confusion about how to use them, can daunt either the writer or the reader, try rephrasing. It’s a guide about how to use hyphens wisely, not it’s a how-to-use-hyphens-wisely guide.

Use a hyphen whenever ambiguity would result if it were omitted. 
e.g. He recovered his health. He re-covered the leaky roof.

Use a hyphen if it’s needed to make the meaning clear and avoid unintended meanings.
e.g. small-business owner, better-qualified candidate, little-known warbler

Other two-word terms, particularly those used as nouns, have evolved to be commonly recognized as, in effect, one word. No hyphen is needed.
e.g. climate change report, public land management, real estate transaction

Em dashes

Note: we do not leave spaces on either side of an em dash, contrary to AP’s style.

Use to denote an abrupt change in thought in a sentence or an emphatic pause: Through her long reign, the queen and her family have adapted—usually skillfully—to the changing taste of the time. But avoid overuse of dashes when commas would suffice.

When a phrase that otherwise would be set off by commas contains a series of words that must be separated by commas, use dashes to set off the full phrase: He listed the qualities— intelligence, humor, conservatism, independence—that he liked in an executive.


Use standard measurements except in special cases such as scientific articles, where metric measurements may be substituted. Pay attention to discrepancies between the U.S. ton (the “short ton,” measuring 2,000 lbs), the British ton (the “long ton,” measuring 2,240 pounds) and the tonne (the “metric ton,” measuring 2204 pounds).

million, billion
In the usual form: 5 million, 10 billion. In adjectival form, hyphenate throughout: 300-million-acre parcel, 5-million-gallon tanker. In the case of dollar, sterling sums: $500 million, ₤5 billion.

Pair the symbol (%) with the numeral. Avoid starting a sentence with a percentage—but write out the words if you must. 

Spelling out vs numerals
In general, spell out whole numbers below 10, and use numerals for 10 and above. Note an exception in guidance on percentages.

Headlines can allow numerals below 10 and at the start of a sentence/clause.

* Fractions with a decimal are numerals: 2.5 inches.
* For ages, always use numerals: 5 years old.
* For dimensions, use numerals to indicate depth, height, length and width, hyphenating adjectival forms. Examples:

5-foot-6-inch player 5 inches of snow
6 feet long

Telephone Numbers
Contrary to AP, use only dashes, no parentheses: 703-841-5300.

Using dashes allows numbers to be clickable on nature.org.

For international numbers, the number of numerals may vary, e.g., 62-21-544-631

Honorifics and titles

Academic titles 
Avoid titles unless requested by the individualIf requested, use “Dr.” on first reference, citing the specific area of expertise if relevant. For subsequent references, use only the individual’s surname.

Other honorifics and courtesy titles (e.g. Ms., Mr., Miss, professor)
Avoid unless requested by the individual.