The Toulmin Model has traditionally been used as a framework for discerning the structure of an argument and as a model for analyzing the relations among the elements in an argument. In recent years, many advocates have claimed that the model can serve as a foundation for cultivating argumentation abilities. Furthermore, some studies have mentioned benefits from using the Toulmin Model, such as allowing for due consideration of the uncertain elements in everyday logic and making easy-to-overlook problems more obvious by differentiating between the evidence and the reason within the argumentation process. However, despite these benefits, the following questions have also arisen:

(1) Why is Backing (B) required for Warrants (W), but not for Datum (D)?

(2) Should the attachment of Qualifiers (Q) and Rebuttal (R) to Datum (D) and Warrants (W) depend on the situation?

(3) Can Backing (B) be regarded as corresponding to Datum (D) when considering Warrants (W) as one Claim (C)?

These questions suggest that there is room for modification in the model's six-item layout.

Aiming to answer these questions, this paper argues for the following four conclusions with respect to questions (1) and (2). First, as a consequence of Warrants (W) being hypothetical statements and implicitly demonstrated elements, Backing (B) elements are necessary to categorically prove that Warrants (W) are justifiable. Second, since Warrants (W) are broad facts that retain a degree of ambiguity inherent within conjectures and interpretations, Backing (B) can reduce the ambiguity of Warrants (W) themselves, and increase their certainty, whilst simultaneously providing Warrants (W) with logical grounds as a premise. Third, even if Datum (D) is a categorical statement of a fact, there is a broader assertion that cannot be qualified by this element alone. Fourth, as a consequence of ambiguities that cannot eliminate the latent uncertainties within Warrants (W), adverbial phrases such as “probably” and “perhaps” should be required as Qualifiers (Q).

Based on these conclusions, this paper proposes a new layout of the Toulmin Model for the process of argumentation, by discussing, among other topics, whether it is possible to treat Datum (D) as a categorical statement of fact or Warrants (W) as universal propositions.

国際課税の主要な課題が国際的二重課税と国際的租税回避から国際的二重非課税にシフトした結果として、現在、「税源浸食と利益移転」（BEPS）が世界的に大きな政治・社会問題となっている。OECDは、多国籍企業のグローバル化と経済の電子化による国際的二重非課税に起因するBEPSに対処するために2015年10月に「BEPS最終報告書」を公表し、11月のG20財務大臣会議で採択されている。その後、OECDは経済のデジタル化から生じる税制上の課題に対処するために、「BEPSに関するOECD/G20包摂的枠組」（「BEPS包摂的枠組」）を2016年に設置し、BEPSに対する解決策の基礎を形成する可能性のある2つの柱の青写真に関する報告書を2020年10月に公表した。「第1の柱」は、すべての管轄地域間で公平な競争条件を確保し、課税権のより公平かつ効率的な配分を実現するために、事業利益に適用される課税根拠と利益配分に焦点を当てる。「第2の柱」では、国際的に営業している大規模事業者が少なくとも最低レベルの税金を支払うことを保証するために、最低法人税率の全世界的導入が提案されている。

本稿では、「BEPS包摂的枠組」によって2020年10月に承認されたBEPSに関する2つの柱の青写真に関する報告書（「第1の柱」と「第2の柱」）のうち、「第2の柱」の内容・特徴および2021年10月のG20最終合意を解析した上で、国際課税の課題（BEPS）が理論的に探究される。