Id. (masculine and neuter) and ead. (feminine) (Latin, short for idem and eadem, "the same") denote the previously cited source (compare ibid.). Id. is particularly used in legal citations. They are also used in academic citations replacing the name of a repeated author. Id. is used extensively in Canadian legislation and in legal documents of the United States to apply a short description to a section with the same focus as the previous.
Contents
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 (see usage of the full stop in abbreviations). Its first known use dates back to the 14th century.
Legal examples
Here, the first citation refers to the case of United States v. Martínez-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. Id. refers to the immediately preceding citation, so if the previous citation includes more than one reference, or it is unclear which reference Id. refers to, its usage is inappropriate.
Here, Id. refers to the Executive Order that was mentioned in the previous sentence.
Academic example
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.