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A citator is an index that works backwards: instead of listing what a case cites, it lists every later case, statute or other document that cites it, and tells you how those later authorities treated it. Lawyers use citators to confirm a case is still good law, to find later decisions on the same point, and to trace how a rule has developed.
If you learned research on Westlaw, you know it as KeyCite. If you learned on Lexis, you know it as Shepard's, and you probably still say "Shepardize" whichever platform you use. This article explains what both do, where the idea came from, what the signals mean, and how the newer automated citators compare.
A short history
Frank Shepard began publishing citation lists in Illinois in 1873. The first product was a set of gummed labels listing, for each reported case, the later cases that cited it. Lawyers stuck the labels in the margins of their reporters. That was the whole innovation: someone read every new opinion, noted every case it cited, and published the list.
Shepard's Citations grew into a set of bound volumes and supplements covering every reporter, with a code of letters indicating treatment: "o" for overruled, "d" for distinguished, "f" for followed, and so on. Checking a case meant pulling several volumes and paper supplements and reading the entries in sequence, which is why the process had its own verb.
LexisNexis acquired Shepard's and put it online. West responded in 1997 with KeyCite, built on its own editorial staff and integrated with the West key number system. Since then the two have been the standard, and "run it through the citator" has been a step in every competent brief.
The rise of free case law corpora in the last fifteen years, first through Google Scholar and the Caselaw Access Project and then through CourtListener, made automated citators possible: software that extracts citations from every opinion in a corpus, links them, and classifies the treatment by reading the surrounding text. The Frix Law Library citator is one of these.
What a citator tells you
A full citator report for a case has three parts.
Direct history. What happened to this case in this litigation: appeals, affirmances, reversals, remands, certiorari petitions. Also called subsequent history or appellate history. This is what goes in the citation parenthetical.
Citing references. Every later case, and sometimes statutes, regulations, briefs, law review articles and secondary sources, that cited the case. On a commercial platform this list can run to thousands of entries for a leading case, which is why filtering matters.
Treatment. For each citing reference, how it treated the case. This is where the editorial work lives. The main categories, in roughly descending order of severity:
| Treatment | Meaning |
|---|---|
| Overruled | A court with authority to do so held the case is no longer law, in whole or in part |
| Abrogated or superseded | A later decision or statute removed the basis for the holding without formally overruling it |
| Reversed or vacated | Direct history: the decision was undone on appeal |
| Criticised or questioned | A later court expressed doubt but did not overrule |
| Limited | A later court confined the holding to its facts or narrowed it |
| Distinguished | A later court found the case inapplicable to different facts |
| Followed | A later court applied the holding |
| Cited or discussed | Mentioned without evaluation |
Signals and flags
Both commercial citators summarise treatment with an icon at the top of the case. The details differ but the colour logic is shared and has become an industry convention.
Red indicates that at least one point of law in the case has been overruled, reversed or otherwise held no longer good. It does not mean the whole case is dead. Both Shepard's and KeyCite try to indicate which headnote or point was affected, and you have to read the citing decision to know whether it touches the point you need.
Yellow indicates negative treatment short of that: the case has been criticised, distinguished, limited or questioned, or there is a conflicting line of authority. A yellow signal on a heavily cited case is normal and often harmless.
Both platforms also have signals for pending appeals, positive treatment, and cases that rely on overruled authority. The specifics are documented on each platform and change from time to time, so check the legend rather than trusting memory.
Depth of treatment
A citing reference that mentions your case in a string cite is different from one that spends three pages on it. Editorial citators indicate this. KeyCite shows a depth-of-treatment indicator for each citing case, from a passing mention to an extended discussion. Shepard's provides analysis phrases and lets you filter by treatment type. Both let you narrow to citing references that discuss a particular headnote.
Depth is the most useful filter when a case has hundreds of citing references. Start with the ones that treat it in depth and negatively, then in depth and positively, and skip the string cites.
Editorial versus automated citators
The commercial citators employ editors who read citing opinions and classify treatment. The automated ones classify by software, typically by extracting the sentence in which the citation appears and reading the language around it for signals like "overruled", "we decline to follow", "distinguishable" or "abrogated by".
The practical differences:
- Coverage of implicit overrulings. When a court overrules a case without naming it, or overrules a line of authority by rejecting its reasoning, editors catch it more often than software does. Automated citators can miss these entirely.
- Headnote-level analysis. Editorial citators tie treatment to specific headnotes. Automated citators generally work at the level of the whole case.
- Speed and cost. Automated citators update as soon as a new opinion enters the corpus and cost nothing. Editorial classification takes longer and is what you pay for.
- Transparency. Automated citators can show you the exact citing sentence and let you judge for yourself. Editorial ones summarise, and the summary is sometimes all you see until you open the case.
The right way to use an automated citator is as a finder, not a judge. It will tell you which citing cases to open. You decide what they mean.
How to read a citing references list
Whatever citator you use, the process is the same.
- Filter to negative treatment first. Read every entry. For each, find the passage in the citing opinion and decide whether it reaches your point and whether the citing court binds yours.
- Then look at the most recent citing cases from binding courts. A recent, positive citation from your circuit or state supreme court is the strongest evidence a case remains good law.
- Check whether the case rests on authority that has itself been overruled. Citators do not always propagate this.
- If the case interprets a statute or rule, check the statute separately. Citators mark superseding legislation inconsistently.
For the full step-by-step check, see how to check whether a case is still good law.
Limitations of every citator
- Citators only know about documents in their corpus. A treatment in an unpublished state trial court order that was never collected will not appear anywhere.
- Classification is a judgment. Two editors can disagree about whether a case was "distinguished" or "limited", and software disagrees with both.
- A citator cannot tell you whether a case is persuasive, well reasoned, or likely to be followed. It tells you what has happened, not what will.
- Statutes and regulations are covered less thoroughly than cases on every platform.
The Frix citator
The Frix Law Library runs an automated citator over its 10.8 million opinions. On each case page, a red flag means a citing case reports the decision was overruled, reversed, vacated or abrogated; a yellow flag means it was criticised, distinguished, limited or questioned. The citing references list shows the sentence in which each later court cited the case and a short parenthetical, so you can see from the list which references deserve a click.
It is free and needs no account, and Donna will run it for you if you ask a question at /ask. It is automated, not editorially reviewed, and it does not do headnote-level analysis, so it is a finder in the sense described above. Read the citing case. For how this compares with the commercial products, see Frix vs Westlaw and Frix vs LexisNexis.
Quick answers
Frequently asked questions
A citator is a reverse index of legal authority. For a given case, statute or regulation, it lists every later document that cited it and, in editorial citators, classifies how each one treated it, so you can tell whether the authority is still good law.
Frix · Editorial team
We write about legal research and running a small firm. Every case and statute we mention links to its record in the free Frix Law Library, so you can read the source yourself. This is general information, not legal advice for any matter.