A technology arrives that the profession does not know how to think about, and the response follows a reliable sequence. First the anecdotes, then the sanctions, then the committees, and, at last, the question of whether a new body of law is required.
Hallucinated citations have now carried us to the fourth stage, and bar associations, courts, and firms are all busy, in committees, orders, and blog posts, drafting proposals on what should be done.
This sequence is not new, and the profession already witnessed it unfold, with the same sound and fury, after the arrival of the world wide web.
In 1996, at a conference convened to consider the law of “cyberspace,” Frank Easterbrook advised the assembled participants that their subject did not warrant a body of law of its own. Invited to speak on property in the age of the internet, Easterbrook reported that his first instinct had been to wonder whether this was simply the law of the horse in new dress. As Easterbrook noted, the formulation came to him from Gerhard Casper. As dean of the University of Chicago Law School, Casper had boasted that his school taught no such course.[1] Equine disputes scatter across sale, tort, licensing, and professional negligence, and, consequently, any attempt to gather them into a subject of their own is, in Easterbrook's words, "doomed to be shallow and to miss unifying principles."[2] Accordingly, Easterbrook provided the prescription: "Develop a sound law of intellectual property, then apply it to computer networks."[3]
There is no law of the hallucination
Let's set memories of ‘90s dial-up aside for a moment to point out what a lawyer has actually done when a brief goes out bearing citations to cases that do not exist. Essentially, that lawyer has signed a document they did not read.
The profession has rules for that, and they are neither obscure nor recent. A lawyer who signs a filing certifies that the legal contentions it advances are warranted by existing law.[4] Competence has always been understood to require the thoroughness and preparation necessary for the representation.[5] Candor toward a tribunal forbids a knowing false statement of law and imposes an affirmative duty to correct one already made.[6] And the rules governing supervision extend the same logic to work a lawyer has delegated to someone (or something) else.[7]
None of these duties contains an exception for text the signing lawyer did not personally compose, and none ever has. The profession has never accepted "the summer associate drafted it" as an answer (regardless of whether that summer associate was a younger version of this author getting lost on the subway on the way to the office, on one end of the spectrum, or an associate on the masthead of the Yale Law Journal, on the other end of the spectrum), and nothing about the drafter being a machine rather than a second-year alters the structure of the obligation. A rule addressed specifically to generative artificial intelligence would add nothing the signature block does not already supply.
Easterbrook had made the same observation about copying. Cheaper copying, he allowed, "may make violations of the law more attractive," and may warrant spending more to catch the violators, "but movement along a cost continuum does not call for change in legal substance."[8]
If this is the case, then, why are courts and bar associations frantically scribbling guidance for practitioners, if the practice already has a strong layer of rules that apply to hallucinations?
What Lessig saw
Lawrence Lessig published his answer to Easterbrook years afterward, and the striking feature of that answer is that it does not proceed by defending the law of the horse. Lessig concedes most of the frame at the outset, and concedes it in terms that leave him very little room: "I am not defending the law of the horse. My claim is specific to cyberspace."[9]
The claim he does make is that "[b]ehavior... is regulated by four kinds of constraints" rather than one: law, social norms, the market, and what he calls architecture, meaning the structure of the space in which the behavior occurs.[10] Law is the modality lawyers are trained to notice, because law is the modality we think about continuously, being in the profession. However, the other constraints of social norms, market, and architecture also constitute levers of control. For the “cyberspace” of the ‘90s, and for the large language model boom of the 2020s, the design and code of the technologies provide such architecture.
Lessig's own example is worth following, because its shape recurs. He asks the reader to imagine walking into a store where a guard records your name, cameras track which items you look at and which you ignore, and an employee follows you down each aisle timing you. If that happened in a shop, he observes, "you would notice." You might not object. But you would know enough to choose, if you possessed preferences regarding such surveillance.[11]
In “cyberspace” you would not, and the reason is architectural. On the internet, "[s]urveillance is not self-authenticating," Lessig writes; "[n]othing reveals whether you are being watched."[12] No privacy rule was repealed to bring this about. What changed is that the (cyber) space, due to its architecture, stopped supplying (for free) facts about the user's privacy (or lack thereof), which were otherwise provided by nature of browsing a physical store in person. The ordinary condition of the architecture does the regulatory work, independent from any laws.[13]
What Lessig draws out of this is the following proposition: "Cyberspace has no nature; it has no particular architecture that cannot be changed."[14] He means it narrowly. It's not that the present design has no features, but that other designs are possible.
Easterbrook's essay is remembered for its opening about equine law. However, the second half of his essay, about costs, is also relevant to discussions of regulatory architecture. Having declined to prescribe a law of “cyberspace,” he turns to the economics of copying: "Cyberspace reduces the effective cost of copying."[15] Easterbrook noted that copyright already prohibited what the photocopier and then the network made easy. The difficulty is that a right becomes unenforceable when transacting over it costs more than the transaction is worth.[16]
His remedy was design-driven, as opposed to the imposition of law. Each file would carry its own instructions on copying; programs would read those instructions and negotiate automatically; a standards body would publish a menu of options from which parties could choose at low cost.[17] The model he reached for was the Uniform Commercial Code and Karl Llewellyn's vision of giving merchants defaults they could adopt without bargaining for them, Llewellyn being the man who coined "the law of the horse" in the first place, for the amateur trade the UCC was written to leave behind.[18] However, the means by which Easterbrook imagines effectuating his remedy was architectural: protocols built into the code which, by design, make a market for intellectual property.
Accordingly, the judge who told the cyberlaw conference that its subject did not deserve a course spent the rest of his remarks designing an architecture for it! The distance between Easterbrook and Lessig is smaller than the citation history suggests.
Returning to Lessig's view that "Cyberspace has no nature; it has no particular architecture that cannot be changed," the architecture of legal research has no nature either. It has a present design, which is recent and malleable.
The price of an old duty
What was the architecture of a legal citation before large language models arrived?
Until quite recently, the existence of a cited authority was very nearly self-authenticating (using Lessig's language), and the profession had no particular occasion to notice that strange reality. A citation reached a lawyer through a reporter, a treatise, a citator, or a commercial database, and whatever delivered it also vouched for it. To reach print at all, the citation had to pass through someone who had found and read the case, or through a deterministic process overseen by such a person. To reach a brief, from print, it had to pass through a lawyer who located the entry in one of those volumes and copied it out by hand. Human-linked checks therefore occurred, automatically, as part of a lawyer's normal practice, even though those checks were not designed as checks. Additionally, these checks seemed, to the practitioner, free, since the costs of such checks (a publisher sourcing an opinion for inclusion in their product or a lawyer finding and copying a reference to an opinion from such a product) occurred incidentally with regular lawyering (instead of requiring supplementary effort).
A language model severs these automatic checks from the lawyerly day-to-day. A citation can now enter a draft without any publisher having collected it and without any lawyer having found it, and where the model sits inside the word processor, the citation can enter the draft without anyone having looked at the citation, at all. Worse, the genuine and the invented citations arrive in identical dress (plausibly formatted, plausibly numbered, plausibly named), so a cursory read of the citations will not separate them.
It's worth being careful about what has changed here (and what has not). Today's professional responsibilities regarding citations are largely the same responsibilities that regulated practitioners in 1995. However, in 1995, the additional costs of fulfilling those responsibilities, in proving the existence of a citation, were something near zero, since human oversight occurred automatically as a byproduct of a lawyer's use of a citation in work product. These costs were already bundled in the publishing costs of the reporter, a treatise, a citator, or commercial database, and in the cost of the lawyer's own exertion in reading and copying from those publications.
Flash forward to 2026: the lawyer using a large language model can produce written work product, citations included, while avoiding the previously bundled costs of the publisher and their own toil in reading and transcribing the citations. Because of this unbundling, the additional costs of fulfilling the responsibilities related to the verification of any citation are now substantive, and entirely borne by the lawyer.
That single displacement accounts for a good deal of institutional behavior that otherwise looks reactionary. When firms, courts, and bar committees reach for moratoria, disclosure regimes, and outright prohibitions, they are not responding to any ambiguity in what the profession requires; what the profession mandates, in terms of rules, is largely the same. Instead, they are responding to the economic shift described above: a duty that was seemingly cheap (because the costs were bundled in the nature of production) has become expensive, and one way to manage the now-expensive duty is to forbid the activity that requires it.
Two failures under one name
There is a second difficulty here, which emerges from the purpose of citations in legal writing. Damien Charlotin's database of judicial decisions addressing hallucinated material listed 2,006 decisions as of September 1, 2026, of which 1,376 came from United States courts, sorted into categories. A single decision can carry more than one tag, so the categories overlap (and the totals do not sum). Across the database’s American-tagged items, fabricated authorities appeared in 1,134 decisions. Misrepresented authorities appeared in 586, and false quotations in 462.[19]
Those latter categories describe a different animal altogether. There the case is real, the citation is accurate, and the reporter volume checks out on inspection. However, the proposition attached to the citation has been invented, with language placed in the mouth of a court that never articulated such a position.
Why should that distinction matter so much?
Because whether a case exists is a question of lookup, and lookup is a (relatively) easier category of problem (that's why it was also largely solved by the "automatic" publisher and lawyer checks described above). On the other hand, whether a case holds what it has been said to hold is a question of reasoning (something difficult for a lookup against an index).
This is why a tool that only checks existence and stops there can be more dangerous than a tool that does nothing. Having disposed of the easier half of the problem, it gives the lawyer a state of confidence, even though hallucinations regarding the reasoning of the court may still lurk in the shadows.
Rebuilding the architecture
If the law is already relevant to the problem of hallucinations, let's turn back to Lessig and Easterbrook to see if we can also use architecture to control this emergent problem. For an architecture to regulate citational hallucinations effectively, we must consider questions on how the architecture affects the costs borne by the lawyer to discharge their professional duties.
The work we have been doing at Filevine divides into two layers that together alter these costs.
The first addresses existence. Every citation to a case produced by LOIS is automatically checked against source databases of reporter-based citations. Verified citations are rendered as checkmarked links that open the opinion beside the answer. Unverifiable citations, in contrast, are flagged with caution highlighting and left unclickable.
The second layer addresses the harder failure: hallucinations in legal reasoning. Where the tool relies on a given passage from an opinion, it opens the opinion to that passage and highlights it for the user, so that confirming an assertion becomes an immediate read rather than a lost expedition through seventy pages of judicial writing. Additionally, using this second layer, an attorney can put questions to a single opinion directly. They can ask the opinion what the procedural posture was, how the court reached its conclusion, how far the holding actually extends, or what the dissent was arguing, for example. Those answers come directly from the text of the court opinion, likewise highlighted.
What our architecture changes is the number of steps (i.e., costs) for a lawyer to discharge their professional obligations: the architecture gives the lawyer an amber gloss on top of a problematic citation rather than plain text that masks a hallucination, a click in a panel rather than a new lookup session on another platform, and a jumped-to, highlighted paragraph rather than seventy unmarked pages.
The architecture that once made these duties seemingly free was not designed by anyone; it was a byproduct of how citations happened to reach, and be used by, lawyers. However, because LLM-driven legal research no longer supplies such verification as a byproduct, anti-hallucination architecture must be built on purpose, which we have sought to do.
An old kind of answer
Easterbrook, still on copying, described different modes of regulating reproduction in the 90s internet era. He pointed at the weakness of regulating behavior by fiat, regardless of the economic costs. The Copyright Clearance Center printed a line at the foot of articles directing the copier to remit fifty cents a page. He asked whether anyone actually remits: "No, you don't, because the extent of the fair-use privilege is so hard to grasp, and because remitting would be such a bother—do you tape two quarters to a post card and mail it?"[20] Discharging the obligation was a bother, so it went undischarged, and the Center "barely raises enough money to cover the costs of its operations."[21]
Every prohibition now being drafted for generative research tools is a slug line at the foot of an article. It states an obligation that already existed but neglects the economic costs of the obligation, given the technological change. Some lawyers will pay the fifty cents (i.e., closely read and double-check each citation and claim by hand). Some may not, and hallucinations will thereby cause the chaos observed currently. Rather than more laws and written guidance (slug lines), we propose new architecture, which, by design and function, reduces the costs of discharging the professional obligation so that the lawyer actually does so.
Notes
[1] Frank H. Easterbrook, Cyberspace and the Law of the Horse, 1996 U. Chi. Legal F. 207.
[2] Id. at 207.
[3] Id. at 208.
[4] Fed. R. Civ. P. 11(b)(2).
[5] Model Rules of Professional Conduct Rule 1.1.
[6] Id. Rule 3.3(a)(1).
[7] Id. Rules 5.1, 5.3.
[8] Easterbrook, supra note 1, at 210.
[9] Lawrence Lessig, The Law of the Horse: What Cyberlaw Might Teach, 113 Harv. L. Rev. 501, 502 (1999).
[10] Id. at 506.
[11] Id. at 504.
[12] Id. at 505.
[13] See id. at 506–08.
[14] Id. at 505.
[15] Easterbrook, supra note 1, at 208.
[16] Id. at 208–10.
[17] Id. at 213–14.
[18] Id. at 214 (citing Karl N. Llewellyn, Across Sales on Horseback, 52 Harv. L. Rev. 725 (1939)).
[19] AI Hallucination Cases, https://www.damiencharlotin.com/hallucinations (last visited Sept. 1, 2026).
[20] Easterbrook, supra note 1, at 209.
[21] Id.