Parenthetical referencing, also known as Harvard referencing, is a citation style in which partial citations—for example, "(Smith 2010, p. 1)"—are enclosed within parentheses and embedded in the text, either within or after a sentence. They are accompanied by a full, alphabetized list of citations in an end section, usually titled "references", "reference list", "works cited", or "end-text citations". Parenthetical referencing can be used in lieu of footnote citations (the Vancouver system).
The origin of the author–date style is attributed to a paper by Edward Laurens Mark, Hersey professor of anatomy and director of the zoological laboratory at Harvard University, who may have copied it from the cataloguing system used then and now by the library of Harvard's Museum of Comparative Zoology. In 1881 Mark wrote a paper on the embryogenesis of the garden slug, in which he included an author–date citation in parentheses on page 194, the first known instance of such a reference. Until then, according to Eli Chernin writing in the British Medical Journal, references had appeared in inconsistent styles in footnotes, referred to in the text using a variety of printers' symbols, including asterisks and daggers. Chernin writes that a 1903 festschrift dedicated to Mark by 140 students, including Theodore Roosevelt, confirms that the author–date system is attributable to Mark. The festschrift pays tribute to Mark's 1881 paper, writing that it "introduced into zoology a proper fullness and accuracy of citation and a convenient and uniform method of referring from text to bibliography." According to an editorial note in the British Medical Journal in 1945, an unconfirmed anecdote is that the term "Owen system" was introduced by an English visitor to Harvard University library, who was impressed by the citation system and dubbed it "Harvard system" upon his return to England.
Although it originated in biology, it is now more common in humanities, history, and social science. It is favored by a few scientific journals, including the major biology journal Cell.
In the author–date method (Harvard referencing), the in-text citation is placed in parentheses after the sentence or part thereof that the citation supports. The citation includes the author's name, year of publication, and page number(s) when a specific part of the source is referred to (Smith 2008, p. 1) or (Smith 2008:1). A full citation is given in the references section: Smith, John (2008). Name of Book. Name of Publisher.
The structure of a citation under the author–date method is the author's surname, year of publication, and page number or range, in parentheses, as in "(Smith 2010, p. 1)".
Following is an explanation of the components, where the coloring is for demonstration purposes and is not used in actual formatting:
Heilman, J. M. and West, A. G. (2015). Journal of Medical Internet Research, 17 (3), p.e62. doi:10.2196/jmir.4069.
In giving the city of publication, an internationally well-known city (such as London, The Hague, or New York) is given as the city alone. If the city is not internationally well known, the country (or state and country if in the U.S.) is given.
In the author–title or author–page method, also referred to as MLA style, the in-text citation is placed in parentheses after the sentence or part thereof that the citation supports, and includes the author's name (a short title only is necessary when there is more than one work by the same author) and a page number where appropriate (Smith 1) or (Smith, Playing 1). (No "p." or "pp." prefaces the page numbers and main words in titles appear in capital letters, following MLA style guidelines.) A full citation is given in the references section.
A content note generally contains useful information and explanations that do not fit into the primary text itself. Content notes may be given as footnotes or endnotes or even a combination of both footnotes and endnotes. Such content notes may themselves contain a style of parenthetical referencing, just as the main text does.