Preserving Decision Authorship under Uncertain Interpretation of Will and Preferences in Adult Disability Support

Assistance can make a person's decision possible while leaving the person vulnerable to interpretive substitution and control of the available options. This paper develops a framework for adult disability support when will and preferences admit several warranted interpretations. Decision authorship is distinguished from causal responsiveness, functional performance, legal capacity, the validity of a particular act, and responsibility. A set-valued model separates semantic fidelity from authority over support and menus. Conditional results characterize compatible outcomes under interpretive uncertainty, changes under additional evidence, and the limited relation between menu expansion and compatibility. Counterexamples show that reversing every expressed preference satisfies sensitivity, that a constant outcome can satisfy fidelity, and that accurate selection within a restricted menu can coexist with an objectionable exclusion of alternatives. A temporal extension distinguishes learning about an earlier preference from forming a present preference through support. A finite branchwise result identifies when clarification permits compatible implementation despite an empty initial intersection. The normative discussion confronts CRPD Article 12, the Committee's corrected General Comment No. 1, selected provisions of the Mental Capacity Act 2005, and a prior proposal for interpretive support. A fictional community-participation decision demonstrates the audit, including disagreement, refusal, revision and supporter conflict. The resulting framework makes uncertainty and authority answerable without converting mathematical compatibility into permission to decide for another person. Empirical validation and case-specific legal application remain open.