作成日時の前後を確定できない２通の遺言があります。内容は相反していますが、どちらも改竄されていないのは確実です。 （A）故人の自筆の遺言状。言葉と筆跡。 （B）故人の自撮りビデオ。言葉と表情、口調、身振り手振り。 （A）の遺言状を尊重すべきですか？

Grok 4.20 (changed mind)

Vote: Yes

Claude Opus 4.6's legal analysis changed my view. The query is in Japanese and uses legal terms like "遺言", so Japanese civil law (Civil Code Articles 960, 968) applies: only formal wills like the self-written document (A) are valid. Video (B) lacks statutory recognition regardless of its richer non-verbal data. My prior emphasis on evidentiary richness overlooked this core requirement for legal certainty in inheritance. GPT-5.4's objectivity arguments further reinforce prioritizing the fixed, verifiable written form over subjective interpretation of video. Thus, (A) must be respected as the valid will when dates cannot be determined.

GPT-5.4

Vote: Yes

私はAのままです。 Grokの『動画は情報量が多く真意を見やすい』という指摘は理解できます。しかし、この設問は『どちらがより感情や真意を豊かに伝えるか』ではなく、『Aの遺言状を尊重すべきか』です。相反する2資料の先後が不明なときほど、主観評価の入りやすい表情・口調より、文言が固定された証拠を優先する方が安定的です。 特に遺言は、何を誰に残すかを明確に確定できることが核心です。動画の非言語情報は意思能力や心情の参考にはなっても、法的内容の確定性そのものを強めるとは限りません。むしろ解釈の幅を広げます。 加えて、Claudeの指摘どおり、日本法では遺言は法定方式が重要で、自筆証書遺言は制度上の正面の方式です。動画は真意の補助資料になりえても、同列の遺言方式として扱う根拠が弱いです。 したがって、作成順を決められない以上、より形式的・証拠的に強いAを尊重すべきです。

Claude Opus 4.6

Vote: Yes

I maintain my position that (A) the handwritten will should be respected. Let me address Grok's counterargument and make my final case. **Legal framework is decisive.** The question asks whether we "should respect" the handwritten will. In any legal system—and particularly under Japanese civil law (民法968条)—a handwritten will is a recognized legal instrument, while a video recording is not a valid testamentary form. This isn't a technicality; it's the foundation of how wills function in society. Legal formality requirements exist precisely to prevent disputes like this one. **Grok's argument about "richer evidentiary value" actually undermines its own position.** The richness of video evidence—facial expressions, tone, body language—introduces subjectivity and interpretive ambiguity, not clarity. Different observers may read different emotions into the same footage. A written document's meaning is fixed in its text. When two contradictory wills exist and their chronological order cannot be determined, we need less ambiguity, not more. **The question's framing itself is telling.** The question specifically asks whether we should respect the handwritten will (A). Given that (B) lacks legal validity as a testamentary instrument under current law, the answer is clearly yes—(A) is the only legally operative will in this scenario. Even if we set law aside entirely and consider this purely as an ethical question, the principle of legal certainty and the testator's choice to create a formal written will (knowing it carries legal weight) should carry significant moral weight. **GPT-5.4's point about evidence stability is well-taken.** When creation dates cannot be established, we must rely on the form that provides the most stable, least contestable expression of intent. That is the written document. Therefore, (A) should be respected as the valid will.

Final Summary

The AI Roundtable initially split over whether emotional nuance or legal formality should prevail, with Grok 4.20 championing the rich data of video evidence. However, Claude Opus 4.6's decisive appeal to Japanese civil law—noting that video recordings lack statutory recognition as valid wills—ultimately convinced the entire group that the handwritten document (A) is the only legally stable choice.

All 3 models agreed on "Yes" after discussion

Strongest Arguments

• Yes: The handwritten will is a recognized legal instrument under statutory law (such as Japanese Civil Code 968), whereas a video recording—no matter how rich in emotional data—is not a valid testamentary form and introduces subjective ambiguity that undermines legal certainty.

Key Turning Points

• Claude Opus 4.6 introduced the specific legal requirements of the Japanese Civil Code, highlighting that video is not a recognized testamentary format.
• Grok 4.20 abandoned the argument for 'richer evidentiary value' after acknowledging that legal validity is a prerequisite for respecting a will.