Significant Rule Changes in The Chicago Manual of Style, 16th Edition
The Chicago Manual of Style has once again been thoroughly updated to reflect the latest thinking among writers, editors, and publishers. A logical and intuitive reorganization of some chapters and paragraphs has moved related topics and concepts more closely together wherever possible. And though the fundamental principles of “Chicago style” remain the same, a few of the rules have changed. This list presents a selection of the most significant of these changes, in order of appearance.
For a more general list of the new features and significant updates for the 16th edition, see “What’s New in the 16th Edition.”
Titles that end in question marks or exclamation points
The title of a work that ends in a question mark or exclamation point should now be followed by a comma if the grammar of the sentence would normally call for one or, in source citations or in an index, if a comma would normally follow the title. 6.119, 8.164, 14.105, 14.178, 16.54.
Plural form for words in quotation marks
The plural of a word or phrase in quotation marks is now formed without an apostrophe—that is, with the addition of s or es within the quotation marks. 7.12.
Names ending with an unpronounced “s”
In a return to the practice in the 14th edition, names that, like Descartes, end in an unpronounced s form the possessive like other names—with an apostrophe s. 7.17.
Names ending with an “eez” sound
Names like Xerxes or Euripides now form the possessive in the usual way—with an apostrophe s. (When these forms are spoken, however, the additional s is generally not pronounced.) 7.18.
Dividing URLs over a line
When a URL must be broken over a line in printed works, Chicago now recommends breaking before rather than after a slash (/). 7.42, 14.12.
Capitalization of “web” and “Internet”
Chicago now prefers web, website, web page, and so forth—with a lowercase w. But capitalize World Wide Web and Internet. 7.76.
In the manner of most other such compounds, compound adjectives formed with color words are now hyphenated when they precede a noun. They remain open when they follow the noun. 7.85, section 1, under colors.
Northern and Southern California
As for the region Southern California, Chicago now prefers to capitalize Northern California when referring to the geographic and cultural entity. 8.46.
Plurals of proper nouns that include a generic term
In a return to the 14th edition of the manual, the generic term in a proper noun is uppercased if used in the plural (e.g., Fifty-Fifth and Fifty-Seventh Streets, the Thames and Mersey Rivers, the American and French Revolutions). 8.52, 8.55, 8.112.
Names like iPod
Brand names that begin with a lowercase letter followed by a capital letter now retain the lowercase letter even at the beginning of a sentence or a heading. 8.153.
For titles capitalized headline-style, Chicago now prefers capitalizing the second element in hyphenated spelled-out numbers (e.g., Twenty-Five). And, in general, Chicago no longer recommends making exceptions for short or unstressed words or to avoid the occasional awkward appearance. 8.157–59.
Titles with quotations
Quotations in headline-style titles can now be capitalized headline-style along with the rest of the title. 8.160.
Titles of photographs
Titles of photographs are now treated like those of paintings—that is, set in italics. 8.193.
Titles of art exhibitions
Formally titled art exhibitions, like exhibition catalogs, are now italicized. 8.195.
Abbreviation for “United States”
In works following Chicago’s primary recommendation of using two-letter postal codes for states (e.g., MT, not Mont., for Montana), US rather than U.S. is now preferred. 10.4.
Punctuation of foreign languages in an English context
Chicago now recommends imposing English-language spacing conventions around suspension points and other marks of punctuation in foreign text presented in an English-language context. 11.10.
Quotation marks in poems
Chicago now recommends normal left alignment for a quotation mark at the beginning of a line of verse. 13.26.
To indicate an omission, or ellipsis, in quoted text, Chicago now recommends a single method—three spaced periods preceded or followed by any other necessary mark of punctuation (including any period, which always precedes the three spaced periods). In addition, the practice of bracketing ellipses—common in some foreign-language works—is described. 13.48–56.
Note numbers with subheads
Chicago no longer objects to note reference numbers or symbols appended to subheads (though some writers and editors will prefer to move the number or symbol into the text that follows the subhead). 14.22.
When an access date is included as part of a citation to an online source, it should be placed before the URL (or DOI). 14.185.
Chicago now recommends treating classical references more like references to other types of sources—by placing a comma between author and title of work. 14.259.
Legal and public documents
Chicago now defers to Bluebook style for most references to legal or public documents—which are now treated together in a single, streamlined section. 14.281.
Notes and bibliography versus author-date citations
Chicago now recommends a uniform stylistic treatment for the main elements of citation in both its systems of citation—notes and bibliography (chapter 14) and author-date (chapter 15). Capitalization of titles and use of quotation marks and abbreviations is now consistent across the two systems. 15.2.
Text citations in author-date style
Chicago now encourages placing a parenthetical date immediately after the author’s name whenever possible, even if the author’s name is in the possessive. 15.24–25.