THOUGHT PREDICTION ALGORITHM LEGALITY: ARTIFICIAL INTELLIGENCE, MENTAL PRIVACY, CONSTITUTIONAL RIGHTS AND JUDICIAL ACCOUNTABILITY IN JAPAN

1. INTRODUCTION

Thought Prediction Algorithms refer to artificial intelligence systems designed to infer, estimate or predict an individual's mental states, intentions, preferences, emotional responses or likely decisions using behavioural information, biometric indicators, communication patterns or neurological data.

These technologies may be used in healthcare, recruitment, education, financial services, advertising, security monitoring and behavioural research.

Their use raises significant legal questions concerning mental privacy, freedom of thought, personal autonomy, discrimination, unauthorized surveillance and the reliability of algorithmic predictions.

Japan does not have a separate statute specifically regulating thought prediction algorithms. Instead, their legality is determined through the Constitution of Japan, Act on the Protection of Personal Information (APPI), AI Promotion Act, Civil Code and applicable sector-specific legislation.

An important distinction exists between predicting observable behaviour and attempting to infer an individual's private thoughts or beliefs. The latter may create particularly serious constitutional and privacy concerns.

2. JAPANESE CONSTITUTIONAL FRAMEWORK

A. ARTICLE 13: RIGHT TO PRIVACY AND PERSONAL AUTONOMY

Article 13 protects individual dignity, liberty and the pursuit of happiness.

It provides an important constitutional foundation for privacy and personality rights.

Thought prediction systems that collect or analyse personal behavioural, biometric or neurological information without appropriate justification may interfere with legally protected privacy interests.

B. ARTICLE 19: FREEDOM OF THOUGHT AND CONSCIENCE

Article 19 guarantees freedom of thought and conscience.

This provision is particularly important where algorithms are used to infer political beliefs, religious convictions, ideological preferences or other deeply personal mental characteristics.

Employers, educational institutions and governmental organizations must not assume that algorithmically inferred beliefs provide a legitimate basis for discriminatory treatment.

C. ARTICLE 14: EQUALITY BEFORE THE LAW

Article 14 prohibits discrimination based on race, creed, sex, social status or family origin.

Algorithmic predictions that produce discriminatory outcomes may raise constitutional concerns, particularly where governmental decision-making is involved.

3. STATUTORY REGULATORY FRAMEWORK

A. ACT ON THE PROTECTION OF PERSONAL INFORMATION (APPI)

The APPI is the principal legislation governing the processing of identifiable personal information.

Important provisions include:

Article 17: Specification of purposes of use.

Article 18: Restrictions on use beyond the specified purpose.

Article 19: Prevention of improper use.

Article 20: Restrictions concerning acquisition of personal information.

Article 21: Notification or public disclosure of purposes of use.

Article 27: Restrictions on provision of personal data to third parties.

The Personal Information Protection Commission's guidance specifically recognizes profiling as an activity requiring appropriate specification of processing purposes.

For example, analysing browsing history, purchasing behaviour or personal interests to generate individual credit scores requires appropriate disclosure of the relevant profiling purpose.

Special-care-required personal information, including qualifying medical information, attracts additional statutory protections.

B. AI PROMOTION ACT, 2025

Japan enacted the Act on the Promotion of Research, Development and Utilisation of Artificial Intelligence-Related Technologies (Act No. 53 of 2025).

The legislation establishes a national framework for promoting responsible AI research, development and utilization.

Its objectives include:

Promoting responsible AI development.

Improving transparency.

Addressing risks arising from inappropriate AI use.

Encouraging coordination between government and industry.

Protecting individuals against harmful consequences of AI technologies.

The Act does not establish a comprehensive prohibition on thought prediction algorithms or create a general individual right to explanation of every algorithmic prediction.

C. CIVIL CODE OF JAPAN

Article 709 establishes tort liability for unlawful infringement of legally protected rights or interests through intentional or negligent conduct.

Article 710 permits compensation for non-economic damage.

These provisions may become relevant where unauthorized thought profiling causes reputational injury, discrimination, psychological harm or privacy violations.

4. LEGAL LIMITATIONS ON THOUGHT PREDICTION ALGORITHMS

The following activities require particular legal scrutiny:

Inferring political or religious beliefs without appropriate justification.

Using neurological or medical information without complying with applicable safeguards.

Predicting employee loyalty or psychological characteristics for discriminatory purposes.

Creating individual behavioural scores without adequately specifying their use.

Sharing inferred mental characteristics with unauthorized third parties.

Using inaccurate predictions to deny employment, financial services or educational opportunities.

Conducting intrusive surveillance without lawful authority.

Consent, where required, must be legally valid. Consent alone does not necessarily make an otherwise unlawful or discriminatory practice permissible.

5. IMPORTANT JAPANESE JUDICIAL DECISIONS AND CASE LAWS

Direct Japanese judicial decisions specifically addressing AI-based thought prediction remain limited. The following decisions establish relevant principles concerning privacy, personal information, surveillance and freedom of thought.

1. Kyoto Prefectural Gakuren Case, Supreme Court Grand Bench, 24 December 1969, 1965 (A) No. 1187

Nature: Direct analogous constitutional authority.

The Supreme Court recognized that individuals possess a constitutionally protected freedom against being photographed without justification.

It held that police photography may be permissible in specified circumstances involving criminal activity, evidentiary necessity and appropriate methods.

Legal significance: Systematic biometric collection and AI-based mental-state inference must be assessed against constitutional privacy protections and the necessity and justification for the collection.

2. Waseda University Student Information Case, Supreme Court, 12 September 2003, 2002 (Ju) No. 1656

Nature: Direct privacy authority.

The Supreme Court held that students' names, addresses, telephone numbers and other identifying information collected for a university lecture were legally protected privacy information.

The university's disclosure of this information to police without prior consent, in the circumstances of the case, constituted a tort.

Legal significance: Organizations using thought prediction systems cannot assume that personal information becomes freely disclosable merely because it was originally collected for a legitimate institutional purpose.

3. Juki Net Case, Supreme Court, 6 March 2008, 2007 (O) No. 403

Nature: Analogous authority concerning digital personal information.

The Supreme Court considered whether the national resident registration network violated constitutional privacy rights.

The Court rejected the challenge on the facts, taking account of the limited nature of the information collected and the safeguards governing its use.

Legal significance: Digital information-processing systems are not automatically unconstitutional. Their legality depends on the nature of the information, purposes of processing, safeguards and risks of misuse.

4. My Number System Litigation, Sendai District Court, 30 June 2020, 2015 (Wa) No. 1632

Nature: Analogous authority concerning personal data profiling.

The Sendai District Court examined constitutional challenges involving the collection and integration of personal identification information under Japan's My Number system.

The Court rejected the asserted constitutional violation in the circumstances presented.

Legal significance: Combining different categories of personal information to construct individual profiles raises important privacy questions. However, the legality of processing must be evaluated against its statutory purpose and safeguards.

5. Oogaki Police Surveillance Case, Nagoya High Court, 13 September 2024, 2022 (Ne) No. 287

Nature: Direct analogous authority concerning surveillance and profiling.

The Nagoya High Court examined the prolonged collection and retention of personal information concerning citizens involved in opposition to a proposed wind-power development.

Police officers had provided information about these individuals to a private company.

The Court recognized substantial privacy violations, awarded damages and ordered deletion of specifically identified information held by Gifu Prefectural Police.

Legal significance: Systematic collection, aggregation and use of personal information can violate privacy even where some underlying information is publicly available. This decision is particularly relevant to predictive algorithms that construct individual profiles from multiple data sources.

6. METI Guidance on Civil Liability in the Utilization and Application of AI, 9 April 2026

Nature: Regulatory guidance, not judicial precedent.

Japan's Ministry of Economy, Trade and Industry published guidance addressing civil liability arising from AI development and use.

It examines responsibility from the perspectives of tort law and product liability, including situations involving AI-supported services and automated systems.

Legal significance: Developers, providers and users may face different liability depending on their respective responsibilities, the foreseeable risks and the circumstances of the damage.

6. LIABILITY AND REGULATORY ENFORCEMENT

Thought prediction algorithms may create legal liability through several mechanisms:

A. PRIVACY VIOLATIONS

Unauthorized collection, disclosure or use of personal information may attract APPI enforcement and civil liability.

B. DISCRIMINATORY DECISION-MAKING

Unfair decisions based on inferred mental characteristics may create claims under applicable equality, employment and civil liability principles.

C. MEDICAL NEGLIGENCE

Where algorithms predict mental or psychological conditions in healthcare, inaccurate predictions or negligent reliance on automated outputs may create professional liability.

D. DEFECTIVE AI PRODUCTS

The Product Liability Act may become relevant where a qualifying defective product causes legally recognized injury.

E. GOVERNMENTAL SURVEILLANCE

Government agencies must comply with constitutional safeguards and applicable statutory authority when collecting and analysing personal information.

7. PRACTICAL COMPLIANCE REQUIREMENTS

Organizations using thought prediction algorithms in Japan should:

Clearly specify the purpose of personal-data processing.

Obtain appropriate consent where legally required.

Apply additional protections to sensitive personal information.

Assess the accuracy and reliability of algorithmic predictions.

Prevent discriminatory uses of inferred mental characteristics.

Maintain appropriate cybersecurity and access controls.

Provide meaningful information about significant profiling activities.

Establish human review of consequential decisions.

Maintain procedures for complaints and correction of inaccurate data.

Conduct periodic legal and ethical assessments.

8. CONCLUSION

Thought Prediction Algorithm Legality in Japan is governed through constitutional privacy protections, freedom of thought, the APPI, the AI Promotion Act and general civil liability principles.

Although Japan does not currently maintain a dedicated statutory prohibition on thought prediction technology, its use remains subject to restrictions concerning personal information, improper processing, discriminatory conduct and infringement of personality rights.

The Kyoto Prefectural Gakuren, Waseda University, Juki Net and Oogaki Police Surveillance decisions provide important judicial guidance concerning privacy, surveillance and digital profiling.

The central legal requirement is that technological ability to predict an individual's thoughts does not automatically create a legal entitlement to collect, infer, store or commercially exploit that person's mental characteristics. Responsible deployment requires lawful data processing, transparency, proportionality, human oversight and effective remedies against harmful algorithmic decisions.