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Citing Sources

Referencing, avoiding plagiarism, and presentation of the Chicago Style


For English-language book titles, the "headline style" is commonly used: the first letters of all words are capitalised,  except for articles (the, a), the prepositions and conjunctions (and, or), to and as. The first word of the title or subtitle is also capitalised.

For non-English titles, it is advisable to follow the conventions of the language concerned, or the syntax if the author is unfamiliar with them. In French titles, only the first word of the title (but not the subtitle) and proper names are capitalised.

For successive entries by the same author or editor, a 3-em dash (followed by a period or comma as in the previous entry) replaces the name(s) after the first appearance.  In the "notes and bibliography" system, titles by the same author are usually listed alphabetically. An initial an or the is ignored in the alphabetical order.  In the "author-date" system, entries are arranged chronologically by year of publication.

The abbreviation ibid. (from ibidem, "in the same place") refers to a single work cited in the immediately preceding note, and should never be used when the preceding note contains more than one citation. It may also be used within one note in successive references to the same work. The Chicago Style prohibits the use of op. cit. with an author’s surname and standing in the place of a previously cited title, sometimes many pages or even chapters earlier because they are “exceptionally unhelpful” and frustrating to the reader. 

Since its 17th edition (2017), the Chicago Style has discouraged the use of ibid. in favour of shortened citations: "Shortened citations generally take up less than one line, so ibid. does not save space, and in electronic formats that link to one note at a time, ibid. risks confusing the reader." (Chicago Book of Style, No. 14.34).