How To list Multiple Sources in Author–Date Citations, Harvard System

Citing Several Sources in a Single Set of Parentheses for Author-Date References
Citing a single source in a parenthetical author-date reference is relatively straightforward in most cases. Whether the source has only one author or several authors, the author name(s) should be provided along with the year of publication: (Smith, 2013) or (Smith, Jones & Thompson, 2012). Depending on the guidelines followed, the punctuation between the final author name and the date might be omitted (Smith 2013), or the word ‘and’ might be substituted for the ampersand when more than one author is involved (Smith, Jones and Thompson, 2012), but the general presentation is the same. However, when two or more references are enclosed within a single set of parentheses, matters are a little more complicated. Punctuation must clearly separate the different sources, which should be arranged in a specific and consistent order when preparing publishable scholarly documents.

If you need to provide references to two or more works by the same author within a single set of parentheses, the dates should be arranged chronologically after the author’s surname and separated by commas. Listing the sources from the earliest publication date to the most recent, as in (Taylor, 1992, 1997, 2001, 2005), or from the most recent publication date to the earliest, as in (Taylor, 2005, 2001, 1997, 1992), will work. The author instructions provided by publishers will sometimes indicate which is preferable, but even if they do not, clustered sources should not be listed in a random or disorganised fashion, so (Taylor, 2001, 1997, 1992, 2005) would never be appropriate. Whichever arrangement you want or need to use should be used consistently throughout your document, including when you list several sources written by the same group of authors in a single set of parentheses: (Smith, Jones & Thompson, 1985, 1997, 2003, 2012). The chronological order used for your in-text citations should match the order used when listing the same sources in your reference list.
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If references to several sources written by different authors are provided within a single set of parentheses, the individual references are normally separated by semicolons and in most cases arranged alphabetically according to the authors’ surnames: (Beedle, 2013; Jacobson, 2011; McNabb, 2001; McNabb & Jones, 1999; Taylor, 1992, 1997). Occasionally, such clustered references are instead arranged chronologically by publication date, usually from the earliest to the most recent publication, so the group of references listed above would take this form: (Taylor, 1992, 1997; McNabb & Jones, 1999; McNabb, 2001; Jacobson, 2011; Beedle, 2013). The order can be inverted, however, placing the most recent publication first. A different arrangement may be required for particular situations and specific reasons – because, for instance, the source actually quoted in a sentence is cited first, though alphabetically or chronologically it would not come first – but otherwise the order chosen should be used consistently throughout a document.

If two or more sources with the same date and written by the same author(s) are cited, they need to be distinguished, and this is generally done by adding a lowercase letter to each date regardless of which author–date referencing style you are using: (Beedle, 2013a, 2013b) and (Smith, Jones & Thompson, 2012a, 2012b, 2012c) are good examples. These letters should appear along with the dates every time you cite the relevant sources as well as in the final list of references so that the in-text citations match and accurately lead readers to the correct sources in your list. In fact, everything about the author and date information provided through in-text references must correspond exactly with the same information in the accompanying list, so author surnames and publication dates should always be carefully compared between the in-text citations and the list of references to ensure absolute accuracy and consistency before you submit your work for publication.

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