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Id. (masculine and neuter) and ead. (feminine) (Latin, short for idem and eadem, "the same") are the terms used to denote the previously cited source (compare ibid.). Id. is particularly used in legal citations. They are also used in academic citations where the term replaces the name of a repeated author. Id. is used extensively in Canadian legislation to apply a short description to a section with the same focus as the previous. Notice that Id. is an abbreviation where the last two letters of the word are not present; thus, it always takes a period (or full stop) in both British and American usage.
- United States v. Martinez-Fuerte, 428 U.S. 543, 545 (1976).
- Id. at 547.
Here, the first citation refers to the case of United States v. Martinez-Fuerte. The volume number cited is 428 and the page on which the case begins is 543, and the page number cited to is 545. The "U.S." between the numerical portions of the citation refers to the United States Reports. 1976 refers to the year that the case was published. The second citation references the first citation and automatically incorporates the same reporter and volume number; however, the page number cited is now 547. It is important to note that Id. refers to the immediately preceding citation. If the previous citation includes more than one reference, or it is unclear which reference Id. refers to, its usage is inappropriate.
- Macgillivray, J. A. Minotaur: Sir Arthur Evans and the Archaeology of the Minoan Myth. New York: Hill & Wang, 2000.
- Id. Astral Labyrinth: Archaeology of the Greek Sky. Sutton Pub, 2003.
In this example, Id in the second citation indicates that the author is identical to that of the previous citation. That is, the author of the second citation is also Macgillivray, J. A.