Tan Hai Peng Micheal and another (as the executors of the estate of Tan Thuan Teck, deceased) v Tan Cheong Joo and another and other matters [2026] SGHC 49

Case Details

• Citation: [2026] SGHC 49
• Court: General Division of the High Court of the Republic of Singapore
• Decision Date: 6 March 2026
• Coram: S Mohan J
• Case Number: Originating Claim No 381 of 2023; Originating Claim No 382 of 2023; Originating Claim No 201 of 2024
• Hearing Date(s): 10, 18 September, 18 November, 3, 9, 15 December 2025
• Claimants / Plaintiffs: Tan Hai Peng Micheal; Tan Hai Seng Benjamin (as the executors of the Estate of Tan Thuan Teck, deceased)
• Respondents / Defendants: Tan Cheong Joo; Tan Seong Kok
• Counsel for Claimants: Yeoh Kar Hoe, Ng Wei Jin and Abel George (David Lim & Partners LLP)
• Counsel for Respondents: Goh Peck San (P S Goh & Co)
• Practice Areas: Civil Procedure; Costs; Artificial Intelligence; Legal Ethics; Personal Costs Orders

Summary

The judgment in Tan Hai Peng Micheal and another v Tan Cheong Joo and another [2026] SGHC 49 represents a seminal moment in Singapore’s judicial response to the integration of generative artificial intelligence (AI) in legal practice. While the underlying dispute concerned the recovery of substantial loans made by the late Tan Thuan Teck (TTT) to the defendants, the proceedings culminated in a significant inquiry into professional misconduct following the citation of fictitious legal authorities in closing submissions. The High Court was tasked with determining the appropriate sanctions for counsel who submitted AI-generated "hallucinations" as legitimate precedents, specifically addressing the non-delegable duties of solicitors to verify the accuracy of materials presented to the court.

The court’s decision reinforces the foundational principle that the administration of justice relies upon the absolute integrity of the materials submitted by legal practitioners. S Mohan J held that the citation of fictitious cases constitutes sanctionable misconduct under the court's inherent jurisdiction and the codified powers in Order 21 Rule 6 of the Rules of Court 2021. The judgment clarifies that the use of AI tools does not absolve a solicitor of their professional responsibility; rather, it necessitates a heightened level of diligence. The court applied the three-stage test from Ridehalgh v Horsefield [1994] Ch 205 to determine whether personal costs orders should be made against the defendants' counsel and the assisting solicitor who prepared the submissions.

Ultimately, the court ordered that the costs of the suits be fixed at a global sum of $180,000, payable to the claimants on an indemnity basis for the portion of the proceedings affected by the fictitious authorities. Furthermore, the court issued personal costs orders against both the counsel on record, Mr. Goh Peck San, and the assisting solicitor, Mr. Sidhu, finding their conduct to be "unreasonable" and "negligent." This decision serves as a stern warning to the legal profession that the convenience of technological tools must never supersede the solicitor’s primary duty to the court and the integrity of the legal system.

The broader significance of this case lies in its contribution to the evolving legal landscape regarding AI ethics. By aligning with recent precedents such as Tajudin bin Gulam Rasul v Suriaya bte Haja Mohideen [2025] 5 SLR 518 and [2026] SGHC 16, the High Court has established a clear doctrinal framework for addressing "AI hallucinations" in litigation. The judgment emphasizes that while the legal profession must adapt to technological advances, the ethical foundations of the practice remain immutable, particularly the duty of counsel to ensure that the court is not misled by fictitious or inaccurate information.

Timeline of Events

1. 6 June 2025: Commencement of procedural milestones leading toward the substantive hearings of the consolidated suits.
2. 2 July 2025: Further interlocutory proceedings and case management directions issued by the court.
3. 7 July 2025: Deadline for specific evidentiary filings and preparation for the upcoming trial dates.
4. 4 August 2025: Filing of further affidavits and bundles of authorities in anticipation of the September hearings.
5. 26 August 2025: Final pre-trial conference to settle the list of issues and the order of witnesses.
6. 4 September 2025: Commencement of the hearing for Originating Claim No 381 of 2023 and related matters.
7. 10 September 2025: Substantive hearing continues; evidence led regarding the loan transactions by the late TTT.
8. 11 September 2025: Cross-examination of key witnesses, including the executors of the estate.
9. 12 September 2025: Conclusion of the first tranche of the hearing; directions given for the filing of closing submissions.
10. 17 September 2025: Defendants file their closing submissions containing the citation of two fictitious authorities (Case A and Case B) at paragraphs 67 and 68.
11. 18 September 2025: Resumption of the hearing; the court and claimants' counsel begin reviewing the defendants' submissions.
12. 4 November 2025: Claimants' counsel identifies that the authorities cited by the defendants do not exist in any legal database.
13. 18 November 2025: Further hearing date where the issue of fictitious authorities is formally raised before S Mohan J.
14. 2 December 2025: Defendants' counsel provides an explanation regarding the use of AI tools and the involvement of an assisting solicitor, Mr. Sidhu.
15. 3 December 2025: Court hears arguments on the potential for personal costs orders against the solicitors involved.
16. 9 December 2025: Final submissions on the "Fictitious Authorities Issue" and the quantum of costs.
17. 15 December 2025: Conclusion of all oral arguments; judgment reserved by the court.
18. 6 March 2026: Delivery of the judgment [2026] SGHC 49, fixing costs and issuing personal costs orders.

What Were the Facts of This Case?

The litigation originated from a series of loan transactions entered into by the late Tan Thuan Teck (TTT) and the defendants, Tan Cheong Joo and Tan Seong Kok. Following TTT's passing, the executors of his estate, Tan Hai Peng Micheal and Tan Hai Seng Benjamin (the Claimants), sought to recover outstanding sums they alleged were due under these loan agreements. The dispute was spread across three separate actions: Originating Claim No 381 of 2023, Originating Claim No 382 of 2023, and Originating Claim No 201 of 2024. These suits were heard together due to the commonality of the parties and the underlying factual matrix involving the late TTT's financial dealings.

The defendants raised several defenses, including the argument that the late TTT was an "unlicensed moneylender" and that the loans were therefore unenforceable under the Moneylenders Act (Cap 188, 2010 Rev Ed). This defense necessitated a detailed analysis of whether TTT fell within the definition of an "excluded moneylender" under the Act. The burden of proof regarding this status became a central point of contention during the trial. In the "First Judgment" ([2025] SGHC 217), S Mohan J found that the defendants had failed to establish any of their defenses and ruled in favor of the Claimants, granting them judgment for the outstanding loan amounts.

The present judgment, however, focuses on a critical procedural irregularity that occurred during the final stages of the litigation. In the defendants' closing submissions, filed on 17 September 2025, their counsel on record, Mr. Goh Peck San, included citations to two legal authorities—referred to by the court as "Case A" and "Case B"—at paragraphs 67 and 68. These cases were cited to support the proposition that the burden of proving that a lender was an "excluded moneylender" rested on the lender (the Claimants) rather than the borrower (the Defendants). Specifically, Case A was purportedly a decision of the High Court of Singapore, while Case B was presented as a supporting authority from a similar jurisdiction.

Upon reviewing the submissions, counsel for the Claimants, Mr. Yeoh Kar Hoe, discovered that neither Case A nor Case B could be located in any reputable legal database, including LawNet, LexisNexis, or Westlaw. Mr. Yeoh brought this to the attention of the court, noting that the citations appeared to be entirely fictitious. This revelation prompted the court to conduct an inquiry into the origins of these citations. It was subsequently revealed that Mr. Goh had engaged another solicitor, Mr. Sidhu, to assist with the research and drafting of the closing submissions. Mr. Sidhu had utilized a generative AI tool to conduct legal research, which resulted in the "hallucination" of the two non-existent cases. Mr. Sidhu admitted to including these cases in the draft provided to Mr. Goh without verifying their existence or accuracy.

Mr. Goh, as the counsel on record, admitted that he had not personally verified the authorities provided by Mr. Sidhu before filing the submissions with the court. He argued that he had relied on Mr. Sidhu’s expertise and that the inclusion of the fictitious cases was an honest mistake resulting from the misuse of technology. The Claimants, however, argued that this conduct was a gross breach of professional duty that had caused them to incur unnecessary costs in attempting to locate and respond to the fictitious authorities. They sought indemnity costs and personal costs orders against both Mr. Goh and Mr. Sidhu.

The factual matrix thus shifted from a debt recovery claim to a significant inquiry into the ethical obligations of solicitors in the age of AI. The court had to examine the internal processes of P S Goh & Co and the nature of the arrangement between Mr. Goh and Mr. Sidhu. The evidence showed that there was no robust system of supervision or verification in place to ensure that AI-generated content was vetted for accuracy. This lack of oversight was central to the court's eventual finding of negligence and the imposition of personal costs orders.

What Were the Key Legal Issues?

The court identified several critical legal issues arising from the "Fictitious Authorities Issue," which required the application of both statutory provisions and common law tests for professional misconduct and costs.

• The Standard of Conduct for Personal Costs Orders: Whether the conduct of Mr. Goh and Mr. Sidhu in citing fictitious authorities met the threshold of being "improper, unreasonable, or negligent" as required under Order 21 Rule 6 of the Rules of Court 2021 and the three-stage test in Ridehalgh v Horsefield [1994] Ch 205.
• The Non-Delegable Duty of Verification: Whether a solicitor on record can delegate the responsibility for the accuracy of court submissions to an assisting solicitor or an AI tool, or whether this duty remains personal and non-delegable.
• Causation and Unnecessary Costs: Whether the citation of the fictitious authorities directly caused the Claimants to incur costs that were "unnecessary" within the meaning of the law, particularly given that the cases were discovered before the court relied upon them.
• The Definition of "Solicitor" under the Legal Profession Act: Whether Mr. Sidhu, who was not the counsel on record but was engaged to assist, fell within the definition of a "solicitor" for the purposes of personal costs orders under the Legal Profession Act 1966.
• The Quantum and Basis of Costs: Determining the appropriate global sum for costs of the entire suits and whether the portion related to the fictitious authorities should be awarded on an indemnity basis.

How Did the Court Analyse the Issues?

The court’s analysis began with a stern reminder of the solicitor’s duty to the court. S Mohan J emphasized that the administration of justice is a "solemn and serious undertaking" that relies on the "absolute honesty and integrity" of the materials presented by counsel. Citing Attorney-General v Shahira Banu d/o Khaja Moinudeen [2024] 4 SLR 1324, the court noted that the system is "vulnerable to being misled if the information is not accurately presented" (at [31]).

The Legal Framework for Personal Costs

The court applied the three-stage test articulated in Ridehalgh v Horsefield [1994] Ch 205 to determine the propriety of personal costs orders:

1. First, the court determines whether the advocate and solicitor has acted improperly, unreasonably, or negligently.
2. Second, the court considers whether such conduct has caused the other party to incur unnecessary costs.
3. Third, the court considers whether it is just in all the circumstances to order the advocate and solicitor to compensate that party for the whole or any part of the relevant costs.

The court noted that this power is codified in Order 21 Rule 6 of the Rules of Court 2021, which allows the court to order a solicitor to personally pay costs that were incurred "as a result of any improper, unreasonable or negligent act or omission" (at [38]).

Stage 1: Improper, Unreasonable, or Negligent Conduct

The court found that the citation of fictitious cases was "sanctionable misconduct" (at [41]). S Mohan J rejected the notion that the use of AI tools provided any excuse for the error. The court held that Mr. Goh, as the counsel on record, had a "non-delegable duty" to ensure the accuracy of his submissions. The court observed:

"Mr Goh, as the counsel on record for the Defendants, undertook that responsibility. In doing so, he had a non-delegable duty to ensure that the submissions were complete, accurate, and properly verified." (at [44])

Regarding Mr. Sidhu, the court found his conduct equally culpable. Despite not being the counsel on record, he was a "solicitor" within the meaning of s 2 of the Legal Profession Act 1966. His failure to verify the AI-generated cases before passing them to Mr. Goh was characterized as a "gross failure" of professional standards. The court noted that the "hallucination" of cases by AI is a well-known risk, and a failure to check the primary sources (the actual judgments) constituted negligence.

Stage 2: Causation of Unnecessary Costs

The court then addressed whether this conduct caused unnecessary costs. The defendants argued that because the fictitious cases were identified early and did not ultimately affect the outcome of the "First Judgment," the costs were trivial. The court disagreed. It noted that the Claimants' counsel had to spend significant time and resources attempting to locate the non-existent cases and then addressing the issue in their reply submissions. Furthermore, the court itself had to expend judicial resources to investigate the matter. The court specifically noted that the issue of whether TTT was an "excluded moneylender" under the Moneylenders Act was a substantive point of law, and the fictitious authorities were intended to mislead the court on the burden of proof (at [55]).

Stage 3: The Justice of the Order

In the final stage, the court concluded that it was just to make the personal costs orders. The court emphasized that such orders serve a dual purpose: compensating the aggrieved party and upholding the standards of the profession. The court referred to Tajudin bin Gulam Rasul v Suriaya bte Haja Mohideen [2025] 5 SLR 518 as the first reported Singapore case on fictitious AI authorities, noting that the present case represented a further evolution of this "concerning trend."

The court also considered the recent decision in [2026] SGHC 16 ("Forbes"), which also involved AI-generated fictitious authorities. S Mohan J noted that while Forbes and Landscape Engineering Pte Ltd v Dot Safety Solutions Pte Ltd [2025] SGHC 214 concerned self-represented litigants, the present case was more egregious because it involved qualified legal practitioners who should have known better (at [29]).

The Non-Delegable Duty and Supervision

A significant portion of the analysis was dedicated to the failure of supervision within the law firm. The court cited Iskandar bin Rahmat v Public Prosecutor [2021] 2 SLR 1151, reminding practitioners that it is their "professional responsibility" to maintain a system of control and supervision (at [51]). The court found that Mr. Goh’s total reliance on Mr. Sidhu, without any independent verification, fell short of the required standard. The court held that the solicitor on record remains "personally responsible" for every word in the submissions filed under their name.

What Was the Outcome?

The court granted the Claimants judgment in the three suits and proceeded to fix the costs. The operative orders were as follows:

"costs of the Suits are fixed at the global sum of $180,000 (excluding disbursements), payable to the Claimants" (at [82])

This global sum of $180,000 was determined after considering the complexity of the three consolidated suits, the length of the hearings (spanning multiple days in September and December 2025), and the work done by the Claimants' counsel. The court also ordered that interest on the costs be payable at the rate of 5.33% per annum from the date of the judgment to the date of payment.

Regarding the "Fictitious Authorities Issue," the court made the following specific orders:

• The costs associated with the discovery and addressing of the fictitious authorities were to be paid by the Defendants to the Claimants on an indemnity basis.
• A personal costs order was made against Mr. Goh Peck San and Mr. Sidhu. They were ordered to personally indemnify the Defendants for the portion of the costs attributable to the fictitious authorities issue, ensuring that the Defendants themselves did not bear the financial burden of their solicitors' negligence.
• The court fixed the specific quantum of the personal costs at $10,000 (inclusive of disbursements) to be paid by the solicitors to the Claimants, representing the additional work necessitated by the misconduct.

The court declined to order the solicitors to pay the entire $180,000 personally, as the bulk of the costs related to the substantive trial which was conducted properly. However, the indemnity basis for the AI-related costs served as a punitive and compensatory measure. The court also noted that while Mr. Sidhu was permitted to bear Mr. Goh's share of the personal costs by agreement between them, both remained jointly and severally liable to the Claimants for that sum.

Why Does This Case Matter?

This case matters because it establishes a clear judicial boundary for the use of generative AI in the Singapore legal system. It is one of the first instances where the High Court has issued personal costs orders against qualified solicitors for "AI hallucinations," moving beyond previous cases that primarily involved self-represented litigants. The judgment serves as a definitive statement that the "AI defense"—the claim that a solicitor was misled by technology—is not a valid defense to a charge of professional negligence or misconduct.

The ratio of the case—that solicitors have a non-delegable duty to verify the existence and accuracy of all authorities cited—is a critical addition to Singapore's civil procedure jurisprudence. It clarifies that the solicitor on record is the ultimate guarantor of the information submitted to the court. This principle is vital for maintaining the "integrity of the administration of justice," a theme that S Mohan J returned to repeatedly throughout the judgment. By citing Attorney-General v Shahira Banu, the court linked the misuse of AI directly to the broader duty of counsel not to mislead the court, even if the misleading is done through negligence rather than intent.

Furthermore, the case highlights the "concerning trend" of AI misuse in litigation, as seen in other jurisdictions. The court referenced Murray (on behalf of the Wamba Wemba Native Title Claim Group) v Victoria [2025] FCA 731, an Australian Federal Court decision, to illustrate that this is a global challenge. By aligning Singapore’s approach with international standards, the High Court has ensured that the local legal profession remains robust against the risks of rapid technological change. The judgment emphasizes that "professional responsibility" must evolve "commensurately" with technological advances (at [29]).

For practitioners, the case is a stark reminder of the financial and reputational risks of inadequate supervision. The imposition of indemnity costs and personal costs orders demonstrates that the court will not hesitate to use its "draconian" powers to deter the citation of fictitious authorities. This serves to protect the court's time and the opposing party's resources from being wasted on "wild goose chases" for non-existent precedents.

Finally, the judgment provides a practical application of the Ridehalgh test in the context of modern technology. It shows that "unreasonable" and "negligent" conduct can be found even in the absence of bad faith, provided there is a "gross failure" to adhere to basic professional standards, such as checking primary sources. This sets a high bar for the "reasonable solicitor" in the age of AI, requiring them to be tech-literate and skeptical of automated outputs.

Practice Pointers

• Non-Delegable Duty: Always remember that the counsel on record bears the ultimate responsibility for the accuracy of every citation in a court filing. This duty cannot be delegated to junior lawyers, assisting solicitors, or AI tools.
• Verify Primary Sources: Never rely on a summary or a citation provided by a generative AI tool without personally verifying the case in a recognized legal database (e.g., LawNet). If a case cannot be found, it must not be cited.
• Supervision Systems: Law firms must implement robust internal systems for supervising the use of AI. This includes mandatory "human-in-the-loop" verification for all research outputs.
• Duty to Correct: If a fictitious authority is discovered after filing, counsel has an immediate and overriding duty to inform the court and the opposing party to correct the record.
• Risk of Indemnity Costs: Be aware that citing fictitious authorities is likely to result in costs being awarded on an indemnity basis, as it is considered a significant departure from the standards of conduct expected of a solicitor.
• Personal Liability: Solicitors should be mindful that the court has the power under Order 21 Rule 6 to make them personally liable for costs, bypassing the client and directly impacting the solicitor’s own finances.
• AI Literacy: Practitioners must understand the limitations of the tools they use, specifically the risk of "hallucinations" in Large Language Models (LLMs), and treat AI outputs as mere starting points for research, not as final products.

Subsequent Treatment

This decision follows the doctrinal lineage established in Tajudin bin Gulam Rasul v Suriaya bte Haja Mohideen [2025] 5 SLR 518 and [2025] SGHC 214. It reinforces the court's zero-tolerance policy toward the citation of fictitious authorities. While it is a relatively recent judgment, it is expected to be the leading authority for personal costs orders against solicitors in the context of AI-generated misconduct, providing a more detailed analysis than the earlier cases involving self-represented litigants.

Legislation Referenced

• Legal Profession Act 1966 (2020 Rev Ed), s 2
• Moneylenders Act (Cap 188, 2010 Rev Ed)
• Rules of Court 2021, Order 1 Rule 3
• Rules of Court 2021, Order 21 Rule 2
• Rules of Court 2021, Order 21 Rule 3
• Rules of Court 2021, Order 21 Rule 6

Cases Cited

• Tajudin bin Gulam Rasul v Suriaya bte Haja Mohideen [2025] 5 SLR 518 (considered)
• [2025] SGHC 217 (referred to)
• [2026] SGHC 16 (referred to)
• [2025] SGHC 214 (referred to)
• Attorney-General v Shahira Banu d/o Khaja Moinudeen [2024] 4 SLR 1324 (referred to)
• Zhou Tong v Public Prosecutor [2010] 4 SLR 534 (referred to)
• Iskandar bin Rahmat v Public Prosecutor [2021] 2 SLR 1151 (referred to)
• Sheagar s/o T M Veloo v Belfield International (Hong Kong) Ltd [2014] 3 SLR 524 (referred to)
• Murray (on behalf of the Wamba Wemba Native Title Claim Group) v Victoria [2025] FCA 731 (referred to)
• Ridehalgh v Horsefield [1994] Ch 205 (referred to)

Source Documents

• Original Judgment (PDF)
• eLitigation Case Summary