14: Notes and Bibliography
Source Citations: An Overview
14.1 The purpose of source citations
Ethics, copyright laws, and courtesy to readers require authors to identify the sources of direct quotations or paraphrases and of any facts or opinions not generally known or easily checked (see 13.1–6). Conventions for citing sources vary according to scholarly discipline, the preferences of publishers and authors, and the needs of a particular work. Regardless of the convention being followed, source citations must always provide sufficient information either to lead readers directly to the sources consulted or, for materials that may not be readily available, to enable readers to positively identify them, regardless of whether the sources are published or unpublished or in printed or electronic form.
14.2 Chicago’s two systems of source citation
This chapter describes the first of Chicago’s two systems of source citation, which uses notes, whether footnotes or endnotes or both, usually together with a bibliography. The notes allow space for unusual types of sources as well as for commentary on the sources cited, making this system extremely flexible. Because of this flexibility, the notes and bibliography system is preferred by many writers in literature, history, and the arts. Chicago’s other system—which uses parenthetical author-date references and a corresponding reference list as described in chapter 15—is nearly identical in content but differs in form. The author-date system is preferred for many publications in the sciences and social sciences but may be adapted for any work, sometimes with the addition of footnotes or endnotes. For journals, the choice between systems is likely to have been made long ago; anyone writing for a journal should consult the specific journal’s instructions to authors (and see 14.3).
14.3 Other systems of source citation
Among other well-known systems are those of the Modern Language Association (MLA) and the American Psychological Association (APA), both of which use in-text citations (described in chapter 15), and that of the American Medical Association (AMA). The AMA uses a numbered list of references cited in the text by reference number; the text numbers appear as superior figures like note reference numbers. Guidelines and examples for these three systems are to be found in the manuals of those associations. Scientific Style and Format, published by the Council of Science Editors (CSE) in cooperation with the University of Chicago Press, also furnishes useful guidelines on both the author-date system and numbered references (see bibliog. 1.1 for these and other style manuals). Many journals and serials—including some of those published by the University of Chicago Press—either follow one of these styles or have their own styles, often based on or similar to the systems mentioned here and in 14.2. For legal and public documents, Chicago recommends The Bluebook, published by the Harvard Law Review Association; see 14.269–305.
14.4 Flexibility and consistency
As long as a consistent style is maintained within any one work, logical and defensible variations on the style illustrated in this chapter and in chapter 15 are acceptable if agreed to by author and publisher. Such flexibility, however, is rarely possible in journal publication, which calls for adherence to the established style of the journal in question. See also 14.3.
14.5 Citation management tools
It is rarely necessary to create a source citation from scratch; even most printed resources will be listed with library catalogs or other online resources. From there, it is easy enough to copy and paste relevant data or to extract them using a number of available tools. Citation management applications such as EndNote or Zotero allow users to build libraries of reference data based directly on their research. These data can be used to place notes or in-text references in a manuscript or to generate bibliographies or reference lists—all formatted according to any number of citation styles (including both of Chicago’s). The results, however, are only as good as the data that generate them and the software used to format them. A few caveats:
- Double-check your data. As you build your library of source data, check each field against the actual source as soon as you acquire the data for it. Make sure authors’ names, titles of works, dates, and so forth are accurate and that they are entered in the appropriate fields. Check also for missing or redundant data. (It is okay, however, to collect more data than you will use in your citations.) You will need to do this whether you entered the data yourself or exported the citation from a library catalog or other resource.
- Double-check your citations. Once a source citation has been inserted in your manuscript, make sure it is correctly formatted according to the recommendations in this chapter or chapter 15. Things to look for include errant punctuation or capitalization and missing or superfluous data. Enter corrections in the citation management application (or adjust its settings, as applicable) and double-check the results in the manuscript.
- Make sure your citations are backed up. Some applications will let you back up your data automatically. It is usually a good idea also to keep local copies as a safeguard. Such backups are helpful not only for ongoing research but also in the event your manuscript must be resubmitted for any reason.
Citation management tools work best for citing recently published books and journal articles and other common publication formats. The variety of sources typically cited in a scholarly work, on the other hand, usually precludes an acceptable result from software alone. Authors are therefore strongly encouraged to review their citations for consistency, accuracy, and completeness before submitting their final manuscripts (editors, in turn, should be aware of how the software works in order to help identify any potential pitfalls). Note also that your publisher may require that such citations be presented as ordinary text, stripped of any of the underlying codes such as fields or hyperlinks used in creating or organizing them. Authors should double-check citations after this conversion to ordinary text and fix any problems both in the text and in the citation data; authors are also advised to save a backup copy of the penultimate version of the manuscript, with codes intact, in case the citations need to be regenerated for any reason. See also 2.22.
Sources Consulted Online
14.6 Electronic resource identifiers
Authors citing sources consulted online should generally include a uniform resource locator, or URL,1 as the final element in a citation that includes all the components described throughout this chapter and in chapter 15. A URL has the potential to lead readers directly to the source cited, and authors are encouraged to include them as part of their source citations (but see 14.11). Many journal publishers, especially in the sciences, create links to sources cited in their articles as a matter of course—a process that authors facilitate when they include electronic resource identifiers with their source citations. Book publishers, on the other hand, may require URLs only in citations of sources that may otherwise be difficult to locate. Authors are therefore advised to consult their publishers early in the publication process. The information in this section—together with the examples of URLs throughout this chapter—is intended to provide guidance for those authors and publishers who wish to include them as part of their research or publications or both. See also 14.7. For citing other types of electronic formats, see 14.159, 14.163, 14.263, 14.265.
14.7 Uniform resource locators (URLs)
A uniform resource locator, or URL—for example, http://www.chicagomanualofstyle.org/—is designed to lead a reader directly to an internet source. Note that it is never sufficient to provide only a URL; as far as they can be determined, the full facts of publication should always be recorded first. Readers should be able to judge the nature and authority of any source from the full facts of publication as detailed throughout this chapter and chapter 15. Moreover, the source to which a URL points is apt to move to a different location or to disappear altogether. For this reason, it is important to choose the version of the URL that is most likely to continue to point to the source cited. For DOIs, see 14.8. For other options, see 14.9, 14.10, 14.11. For URL syntax, see 14.17 and 14.18. For examples of URLs in source citations, see 14.23 (under “Journal Article”) and throughout this chapter and chapter 15.
14.8 Digital Object Identifiers (DOIs)
One of a number of standards addressing the need for more reliable resource identifiers is that of the Digital Object Identifier (DOI).2 A DOI is a unique and permanent string assigned to a piece of intellectual property such as a journal article or book (or a component thereof), in any medium in which it is published. (The term “digital” refers to the identifier and not necessarily to the object.) A DOI forms a persistent URL starting with https://doi.org/ followed by a prefix (such as 10.1086) assigned by a DOI registration agency such as Crossref and then a suffix assigned by the publisher. For example, https://doi.org/10.1086/679716 identifies the article entitled “Scott’s Editing: History, Polyphony, Authority,” by Robert Mayer, published in the May 2015 issue of Modern Philology. This URL will, at a minimum, redirect the user to the latest version of a page with information that identifies the content and includes up-to-date information about its location or availability (from the publisher or other content owner). DOIs are often listed with a source in the form of “DOI:” followed by the prefix and suffix; in their source citations, authors should append this DOI to https://doi.org/ to form a URL as described above. (To find a DOI link or its target, the string starting with the prefix can be entered into the metadata search tool available from Crossref or the DOI resolver provided by the International DOI Foundation.) DOIs are an implementation of the Handle System, which also provides for URLs that begin with https://hdl.handle.net/ and function in much the same way as DOI-based URLs. Authors should prefer a DOI- or Handle-based URL whenever one is available. Examples are included throughout the section on journals (14.168–87) and at 14.161 and 14.234.
2. For more information about DOIs, consult the websites of the International DOI Foundation and Crossref.
14.9 Permalinks and the like
URLs are usually recorded by copying the version of the URL that appears with the source in a web browser’s address bar (or sometimes through a sharing option) as the current link for the reference. Some internet resources list another version of the URL along with the resource itself intended for citing or sharing the link. In the absence of a DOI or the like (see 14.8), these URLs—often labeled as persistent URLs, permalinks, stable URLs, or the like—should generally be preferred. As with any URL, they should be tested to make sure they lead where intended. When a URL points to a location that requires a subscription to a commercial database (e.g., through a library), it may be better to name the database instead (see 14.11).
14.10 Short forms for URLs
A very long URL—one that runs to as much as a line or more of text, especially if it contains a lot of punctuation or other syntax readable mainly by computers—can often be shortened simply by finding a better version of the link. If the source offers a DOI (see 14.8), use that; otherwise, determine whether a permalink or the like is available (see 14.9). If not, it is still often possible to find a better version of the URL, sometimes by relinking to the source using the available tools for navigation. For example, a search for the 1913 novel Pollyanna in the Google Books database may yield a URL that looks like this:
That URL, the result of a search for a specific passage, points to a corresponding page in the book (p. 226). The URL for the main page for the book looks like this (and should be preferred, assuming a page reference is included as part of the full citation):
Alternatively, it is usually acceptable for such formally published resources simply to list the domain name (e.g., https://books.google.com/) or the name of the database (e.g., Google Books); interested readers should be able to search for and find the cited source based on the full facts of publication. On the other hand, shortened versions of a URL provided by third-party services (and intended primarily for use with social media) should never be used. Not only are such services prone to disappear, but the original URL identifies the domain name and other elements that may be important to the citation. Publishers, however, may choose to make an exception, especially for DOIs. (Short forms for DOIs are available through a service from the International DOI Foundation.)
14.11 Library and other bibliographic databases
For a source consulted via a library or other commercial bibliographic database and available only through a subscription or library account, it may be best to name the database in lieu of a URL. Even a URL recommended for such a source (see 14.9) may lead a nonsubscriber to a login page with no information about the source itself. If in doubt, test the URL while logged out of the library or database; a URL that leads to information about the source, if not full access to it, is safe to use. A URL based on a DOI, which will always direct readers to information about the source, if not full access to it, should be preferred where available (see 14.8). For more information and examples, see 14.161 (books), 14.175 (journals), 14.215 (theses and dissertations).
14.12 Access dates
An access date—that is, the self-reported date on which an author consulted a source—is of limited value: previous versions will often be unavailable to readers; authors typically consult a source any number of times over the course of days or months; and the accuracy of such dates, once recorded, cannot readily be verified by editors or publishers. Chicago does not therefore require access dates in its published citations of electronic sources unless no date of publication or revision can be determined from the source (see also 14.13). Because some publishers in some disciplines—in particular, research-intensive fields such as science and medicine—do require access dates, authors should check with their publishers early on, and it never hurts to record dates of access during research (citation management software will do this automatically). (Students may be required to include access dates in their papers.) For examples, see 14.176, 14.207, and 14.233. For access dates in author-date format, see 15.50.
14.13 “Last modified” and other revision dates
Some electronic documents will include a date on each page or screen indicating the last time the document was modified or revised. There are no accepted standards for this practice, and for formally published material the date of publication is generally more important. A revision date should be included, however, if it is presented as the de facto date of publication or is otherwise the only available date. Such dates may be particularly useful for citing wikis and other frequently updated works. For examples, see 14.207, 14.233, 14.234.
14.14 Authority and permanence
Much as they do for printed publications, authors must weigh the authority of any electronic sources they choose to cite. Electronic content presented without formal ties to a publisher or sponsoring body has the authority equivalent to that of unpublished or self-published material in other media. Moreover, such content is far more likely to change without notice—or disappear altogether—than formally published materials. On the other hand, self-published material from an authority on a given subject can usually be relied on. Authors should note that anything posted on the internet is “published” in the sense of copyright and must be treated as such for the purposes of complete citation and clearance of permissions, if relevant (see 4.2, 4.64–69).
14.15 Preserving a permanent record
As part of their research, and in addition to recording accurate and complete source citations as described throughout this chapter and chapter 15, authors are strongly encouraged to keep a copy of any source that is not formally published, as a hedge against potential challenges to the research or data before, during, or after publication. Such a source might include a post on a social-networking site or app, a page from the website of a banking institution, or a version of an article on a news site reporting an ongoing crisis—any source that may be difficult to track down at a later date in exactly the form in which it was consulted. (Examples of sources that would not be subject to this recommendation would include an article in a journal or a magazine or any book cataloged by the Library of Congress or other national registry.) Copies may be kept in the form of printouts or as digital files (e.g., as PDFs or screen captures), or by means of a permanent link creation service such as Perma.cc.
14.16 Publications available in more than one medium
In many cases the contents of the print and electronic forms of the same publication are intended to be identical. Moreover, publishers are encouraged to note explicitly any differences between the two (see 1.78). In practice, because there is always the potential for differences, intentional or otherwise, authors should cite the version consulted. Chicago recommends including a URL to indicate that a work was consulted online. For practical purposes, alternate electronic formats offered by a single publisher from the same URL—for example, PDF and HTML versions of the journal article mentioned in 14.8—do not need to be indicated in the citation. Moreover, a DOI-based URL technically points to each medium in which a work is published. (Though a print source may list a DOI, authors need not record it as part of their research unless their publisher or discipline requires it.) For items designed to be read apart from any website, the application, format, device, or medium should be specified, depending on what might be required to consult a particular version. See also 14.6.
14.17 URLs and other such elements in relation to surrounding text
URLs, email addresses, and the like are unique strings that contain no spaces. URLs should be presented in full, beginning with the protocol (usually http, for hypertext transfer protocol, or https, a version of the protocol that adds support for enhanced security mechanisms). Even if it follows a period, the first letter of the protocol (e.g., the h in http) is not capitalized. (In running text, avoid beginning a sentence with a URL.) The capitalization of the remaining components varies; because some resource identifiers are case sensitive, they should not be edited for style. A “trailing slash” (/), the last character in a URL pointing to a directory, is part of the URL. Other punctuation marks that follow a URL or other such identifier will readily be perceived as belonging to the surrounding text; sentences or citations that include a URL or the like should therefore be punctuated normally. Though angle brackets or other “wrappers” are standard with email addresses or URLs in some applications, these are unnecessary in the context of notes and bibliographies or in running text (see also 6.8).
14.18 URLs and line breaks
In a printed work, if a URL has to be broken at the end of a line, the break should be made after a colon or a double slash (//); before a single slash (/), a tilde (~), a period, a comma, a hyphen, an underline (_), a question mark, a number sign, or a percent symbol; or before or after an equals sign or an ampersand. Such breaks help to signal that the URL has been carried over to the next line. A hyphen should never be added to a URL to denote a line break, nor should a hyphen that is part of a URL appear at the end of a line. If a particularly long element must be broken to avoid a seriously loose or tight line, it can be broken between words or syllables according to the guidelines for word division offered in 7.36–47. Editors, proofreaders, and compositors should use their discretion in applying these recommendations, aiming for a balance between readability and aesthetics.
It is generally unnecessary to specify breaks for URLs in electronic publication formats with reflowable text, and authors should avoid forcing them to break in their manuscripts (see 2.13).
Basic Format, with Examples and Variations
14.19 Notes and bibliography—an overview
In the system favored by many writers in the humanities, bibliographic citations are provided in notes, preferably supplemented by a bibliography. The notes, whether footnotes or endnotes, are usually numbered and correspond to superscript note reference numbers in the text (but see 14.53); in electronic formats, notes and note numbers are usually linked. Notes are styled much like running text, with authors’ names in normal order and the elements separated by commas or parentheses.