When to Use Id. in Bluebook Citations

*Id.* is short for *idem* — "the same." It stands in for the entire preceding citation: source, volume, reporter, court, date, everything. The only thing you may change is the pincite. If anything else about the citation would differ, *Id.* is wrong and you need a different short form or a full cite.

Rule 4.1 states the core condition: *Id.* refers to the immediately preceding authority. In text-based citation (briefs, memos, exams), that means the citation directly before yours, in the same citation sentence, in a citation clause, or in the sentence just above. Intervening prose does not break the chain — you can write three sentences of analysis after citing *Hertz Corp. v. Friend* and still use *Id.* for the next citation, as long as you cited nothing else in between.

The whole thing is italicized, including the period: *Id.* Capitalize it when it begins a citation sentence or a footnote; leave it lowercase inside a citation clause ("..., *see id.* at 40, ..."). Never write "Ibid." — that is Chicago style, not Bluebook — and never write "Id." with a comma before the page number.

Two things. First, any intervening authority. If you cite Case A, then Case B, then want to return to Case A, *Id.* is unavailable; use a case short form (*Hertz*, 559 U.S. at 92) under Rule 10.9, or *supra* for the source types that permit it under Rule 4.2.

Second — and this is the rule journal editors flag most — in footnoted academic work, you may use *Id.* at the start of a footnote only if the immediately preceding footnote contains a single authority. If footnote 12 reads "*Smith v. Jones*, 1 F.3d 1, 5 (1st Cir. 1993); *see also* *Doe v. Roe*, 2 F.3d 2 (2d Cir. 1993)," then footnote 13 cannot begin with *Id.*, even if you mean *Smith*. Two authorities means the reader cannot tell which one "the same" points to. Use *Smith*, 1 F.3d at 7 instead.

Within a single footnote, *Id.* remains available so long as it points to the authority immediately before it. A footnote that reads "*Smith*, 1 F.3d at 5; *id.* at 9" is correct, because *id.* follows *Smith* directly.

If the page is the same as the preceding citation, write *Id.* and stop. Do not repeat the page number. If the page changes, write *Id.* at 412. If the preceding citation had no pincite (a cite to the case as a whole) and you now need one, *Id.* at 412 is still correct.

For footnotes within a source, use *Id.* at 205 n.11. For a source with paragraph or section divisions rather than pages, carry the division symbol: *Id.* ¶ 14; *Id.* § 3.02. For multivolume works where the volume changes, the new volume number precedes the short form: 3 *id.* at 45.

One trap: *Id.* never reaches back to grab a pincite the earlier cite did not have, and it never carries forward an explanatory parenthetical. If you need a parenthetical, write it out again: *Id.* at 412 (explaining that diversity turns on the corporation's nerve center).

Yes, for essentially every source type. *Id.* is the universal short form; the source-specific rules (10.9 for cases, 12.10 for statutes, 15.10 for books, 16.9 for periodicals, 18 for internet sources) all defer to it when the conditions of Rule 4.1 are met.

For statutes, *Id.* § 1983 changes only the section. For regulations, *Id.* § 404.1520(a). For constitutions, *Id.* is the only permitted short form — Rule 11 does not allow *supra* or *hereinafter* for constitutions, so if *Id.* is unavailable you must re-cite in full (U.S. Const. amend. XIV, § 1).

For books and articles, *Id.* at 210 works; if *Id.* is unavailable, drop to the *supra* form under Rule 4.2 (Tribe, *supra* note 14, at 210). Remember that Rule 4.2's *supra* form is unavailable for cases, statutes, constitutions, regulations, and legislative materials other than hearings — so for those, when *Id.* is blocked, you need the source-specific short form or a full cite.

Signals attach normally: *See id.*, *See id.* at 40, *Cf. id.* at 12, *But see id.* Italicize both the signal and *id.* The signal changes the relationship between your proposition and the source; it does not change whether *Id.* is available.

A signal in the preceding citation does not disqualify *Id.* either. If footnote 8 is "*See Erie R.R. Co. v. Tompkins*, 304 U.S. 64, 78 (1938)," footnote 9 may begin *Id.* — one authority, one footnote.

Do not use *Id.* for internal cross-references to your own document. To point the reader to your own earlier or later discussion, use *supra* or *infra* under Rule 3.5 (see *supra* Part II.B), not *Id.*

The substance is the same; Bluepages B4 tracks Rule 4.1. Because practitioner documents put citations in the text rather than in footnotes, the multiple-authority rule usually plays out inside a string cite instead: if your citation sentence ends with two cases, the next sentence's citation cannot be *Id.*

Courts are looser than journals about all of this, and some jurisdictions have local citation rules that displace the Bluebook entirely (California's Style Manual and Texas's Greenbook are the common examples). Check your court's rules and, if you are on a journal, your journal's style sheet — many house styles add or relax conventions, such as permitting *Id.* after a preceding footnote whose only extra content is a cross-reference. Where school or jurisdiction practice varies, the driver is almost always the local court rule or the journal style sheet, not the Bluebook.

A practical drafting habit: because *Id.* is fragile, it breaks whenever you move a paragraph or insert a new citation during editing. Do a dedicated *Id.* pass at the end, checking every *Id.* against the citation immediately above it in the final version of the document.

These are the errors that cost points on a legal writing assignment or get flagged in a journal cite-check.