What does each short form actually do?
*Id.* is Latin for "the same." It tells the reader that the authority you are citing is identical to the one in the citation immediately preceding — same case, same book, same article. If the pincite changes, you add "at" plus the new page: *Id.* at 512. If the pincite is the same, you write *Id.* and stop.
*Supra* means "above." It reaches back past intervening citations to an authority you already cited in full, and it does so by pointing the reader to the footnote where that full citation lives: Sunstein, *supra* note 12, at 1043. It is a navigational device, which is why it depends on footnote numbers and why it is largely useless in documents without footnotes.
The mental test is short. Was the source you want the last thing cited? Use *id.* Was it cited earlier, with something else in between? Then ask what kind of source it is — that answer determines whether you get *supra* or a source-specific short form.
When exactly can you use id.?
Under Rule 4.1, *id.* refers only to the immediately preceding authority. In law review footnotes, that means the preceding footnote must contain only one authority. If footnote 8 cites three sources in a string, footnote 9 cannot open with *Id.* — the reader would not know which of the three you mean. Use a short form naming the source instead.
Within a single footnote, *id.* can refer to the authority cited immediately before it in that same footnote. So a footnote reading: *Miranda v. Arizona*, 384 U.S. 436, 444 (1966); *id.* at 467, is fine.
Intervening explanatory text does not break the *id.* chain; an intervening citation does. If you cite a source, write two sentences of analysis, and then cite the same source again with nothing else cited in between, *id.* still works. Also note that *id.* can follow another *id.* indefinitely — chains of *id.* are normal and correct.
Do not use *id.* after a citation to an internal cross-reference (*see supra* Part II) or after a citation whose antecedent is itself ambiguous. And never write "Id. at Id." or "Ibid." — *ibid.* is not Bluebook.
When can you use supra — and when is it forbidden?
Rule 4.2 permits *supra* for books, treatises, law review articles and other periodicals, unpublished materials, letters, interviews, congressional hearings, and most internet sources. Those are exactly the sources that lack a standardized short-form convention, so pointing back to the full citation is the efficient move.
*Supra* is prohibited for cases, statutes, constitutions, ordinances, regulations, and legislative materials other than hearings. It is also prohibited for restatements, model codes, and similar uniform materials. These sources have their own short forms, and a grader or editor will flag "*Roe*, *supra* note 3" instantly.
The format is: author's last name, *supra* note X, at pincite. Only the word *supra* is italicized — not "note," not the number. If a work has no author, use the title (or an institutional author). If the title is long or the source is awkward to name, assign a short name in the full citation with a bracketed [hereinafter ...] under Rule 4.2(b), then use that name with *supra*.
Separately, *supra* and *infra* are used for internal cross-references to your own document under Rule 3.5: *see supra* Part II.B; *see infra* notes 40–45 and accompanying text. That usage has nothing to do with citing sources and is not restricted by source type.
- Supra OK: Sunstein, *supra* note 12, at 1043.
- Supra OK: Restoring Trust in the Fed: Hearing Before the H. Comm. on Fin. Servs., *supra* note 8, at 22.
- Supra forbidden: any case, statute, constitutional provision, regulation, or restatement.
What do you use instead for cases and statutes?
For cases, Rule 10.9 gives you the case short form: a shortened party name, the volume, the reporter, "at," and the pincite — *Miranda*, 384 U.S. at 467. Use the name of the first-listed non-governmental party; do not shorten to a party name that would confuse ("United States" alone is unhelpful). The Bluebook conditions short-form use on the case having been cited recently — the familiar guideline is that the case must appear in full, or in a short form other than *id.*, in the same footnote or one of the preceding five footnotes. If it has gone stale, cite it in full again.
For statutes, Rule 12.10 lets you drop repetitive elements: 42 U.S.C. § 1983 becomes § 1983 once the reader plainly knows the code you are in. For constitutions, repeat the citation; there is no *supra*.
Practical consequence: if you cite an article, then a case, then want the article again, you use *supra*. If you cite a case, then an article, then want the case again, you use the case short form. The intervening source is what kills *id.*; the source type is what decides your replacement.
How do you format them — italics, capitals, punctuation?
Italicize *id.* including the period, because the period is part of the abbreviation. Capitalize it when it begins a citation sentence (*Id.* at 44.) and leave it lowercase when it appears inside a citation clause or after a signal (*see id.* at 44).
With *supra*, italicize only the word *supra*. The author name and "note 12" stay in roman type. A comma precedes and follows the *supra* phrase: Ackerman, *supra* note 3, at 512.
When the *id.* source has no pages — a statute, for example — carry over the subdivision: *Id.* § 1983. When the pincite is identical to the prior citation, write *Id.* alone. When you need a different volume of a multivolume work, *id.* often will not work cleanly; use the full or *supra* short form.
Does any of this change in briefs and memos?
Yes, and this is where students get burned. Court documents usually have no footnotes, so "*supra* note 12" has nothing to point to. Bluepages B4 keeps *id.* fully functional in briefs and memos — it is the workhorse short form there — but *supra* becomes awkward. Practitioners handle secondary sources either by repeating enough of the citation to be findable or by using a [hereinafter] short name assigned at first mention.
For record citations, briefs use their own conventions (R. 14; Tr. 212:3–9; App. 47), and courts frequently impose local rules that override the Bluebook entirely. Check the court's local rules and any chambers preferences before you assume Bluepages controls.
Note also that the ALWD Guide, used at some schools, tracks the same basic *id.*/*supra* division. If your school uses ALWD, the substance below will hold, but confirm the formatting details against your assigned edition.
What mistakes get flagged most often?
The four errors that cost points in legal writing courses and journal write-on competitions are predictable. First, using *supra* for a case. Second, using *id.* when the preceding footnote holds a string cite. Third, forgetting that the pincite changed and writing bare *Id.* when the reader lands on the wrong page. Fourth, italicizing "note 12" along with *supra*.
A fifth, subtler problem: editing. If you insert a new citation between an authority and a later *id.*, that *id.* now points at the wrong source. Any time you add or delete a footnote, reread the footnotes on both sides of the change. This is the single most common way a clean draft becomes a wrong one.