Home Page > Referencing > Citing Sources by Author and Date


To cite references within a report, place the author’s last name and the year of publication in parentheses:

Recent research (Black 1995) supports this explanation.


Several variations of this basic pattern are described below.

Two or More Publications by the Same Author in the Same Year

If an author has two or more publications in the same year, distinguish between them by appending lower case letters (a, b, c, etc.) to the year of publication (also use these letters after the dates in the reference list):

(Black 1995a; 1995b).

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More than One Author

When a publication has two authors, include both names:

(Smith and Jones 1994).

When a publication has three authors, include all three names the first time you refer to it, but for subsequent references use the first author followed by et al.:


(Smith, Jones, and Brown 1996) for first reference;

(Smith et al. 1996) for subsequent references.

When a paper has four or more authors, cite it as (Black et al. 1993) in the first citation.

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More than One Source Cited

If you give two or more references together, separate them with semi-colons:

(Smith and Jones 1994; Smith et al. 1996).

If you list several sources by the same author, give the name once and then separate the various dates with semi-colons:

(Brown 1986; 1992a; 1992b; 1995).

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No Author Given

When no author is given, but the source is published or sponsored by an association, corporation, government agency, or other group, the name of the group serves as the author’s name (both in the citation and in the reference list). If neither an author nor sponsoring group are indicated, give the name of the publication. In either case, try to make the reference in the sentence rather than within parentheses:

These estimates are based on data provided by the National Research Council (1995).

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Unconventional Sources

For sources such as interviews, personal letters, or mail exchanges, give the full name of the person you communicated with and the nature and date of the communication:

(John Brown, letter to the author, July 1996)
(Bill Smith, telephone interview, 10 Sept 1996)
(Susan Eaglets, mail exchange, Aug-Sept 1996)
(Aaron Bates, email to the author, 4 Nov 1996)

You can create similar citations for films, videos, recordings, television programs, and the like. Do not worry about whether or not you are following the convention because one may not exist. You can always create your own convention, keeping two general principles in mind. First, create a citation that follows the same general pattern as conventional citations. Second, provide similar information to that usually included, but add any additional information readers need to locate the source (either in the citation or in the reference list).

If you are not including a source in a reference list, include all necessary information in your citation. That is, identify the author, artist, director, or appropriate equivalent to an author. Provide the name of the piece or program or another appropriate equivalent to a title. Provide the name of a company, studio, station or other equivalent to a publisher, and, if possible, provide a date of publication or equivalent.

(Buckner and Whittlesey, Directors, Do Scientists Cheat?, Videotape, Boston, MA, WGBH Educational Foundation, 1988)

If you are including a source in your reference list, then the citation should provide the equivalent of an author and a date. If the author is unknown, use the publisher or the title (whatever is available and appears first in your reference list.)

(Buckner and Whittlesey 1988)

Increasingly, research takes us online. While information you acquire from Usenet Newsgroups and the World Wide Web (WWW) home pages may have changed or disappeared by the time someone reads your paper or report, proper citations and references are nevertheless important. When you find information you might use, copy all available information, including author, title, date, name of the newsgroup or home page, Universal Resource Locator (URL), and anything else that might help readers not only find an available source, but also identify a deleted source so that a member of a newsgroup or the owner of a home page will know what the reader wants found.

(XYZ Inc., Thermistor Price List, www.xyz.nz/~thermistors/pricelist/, 22 May 1996)

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Additional Information often Included in Parentheses

Wherever possible, you should assist your reader in finding the information you have cited. To do so, place a volume, page, section, or equation number after the date, separated from the main citation by a comma:

(Smith and Jones 1984, 55) to refer to a single page, or
(Smith et al. 1985, 14-17) to refer to more than one page;
(Brown 1986, sec. 11.5) if an entire section is relevant;
(Black 1987, eq. 10) to refer to an equation.

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Omitting Information from Parentheses

Omit from the parentheses any information already given in the text. For example, if the author’s name appears in the sentence, omit it from the citation. If both the name and date appear in the sentence, you can omit the parentheses or use them only for page, section, or equation numbers:

This method was first proposed by Smith and Jones in 1984 (45-51).

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Placing References Within a Sentence

Wherever possible place your reference at the end of the sentence (or just before a punctuation mark). Readers find it disruptive when the reference is placed between the subject and the verb. This is especially true when the reference is a lengthy one. Often you can revise the structure of a sentence to ensure that lengthy references come at the end.

Sometimes, however, this sort of restructuring is awkward and you may need to place your reference within the sentence. Note, for example, how changing the reference location in the following sentence could result in some ambiguity:

Researchers (Smith and Jones, 1984) have reported findings which support this alternative explanation.

If you put the citation at the end of the sentence, it would appear that Smith and Jones provided the alternative explanation, rather than providing support for it. Consider another example:

Existing methods (Brown, 1986; Black, 1987) fail to account for this potential problem.

Again, both Brown and Black describe existing methods, without necessarily being aware of the problem under discussion. If you put the citation at the end of the sentence, you would suggest that they were concerned with this problem.

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