Decision-making capacity is an increasingly important medico-legal concept. The recent Mental Capacity Act employs a cognitive, process-based test of capacity, but in many psychiatric conditions pathological beliefs and values impair capacity even when the decision-making process is logically coherent. In such cases, capacity assessments implicitly rely on normative epistemic and evaluative standards. This raises a worry for the capacity test’s reliability, objectivity and tolerance of differences in beliefs and values.\ud \ud There is currently little conceptual research on capacity and the normative standards underpinning its assessment. This thesis makes an original contribution to research by employing a number of philosophical approaches to map out a conceptual terrain within which questions about the substantive standards of capacity assessment can be framed.\ud \ud Focusing on the nature of epistemic standards and third-person judgements about decision-making, the thesis examines the normative constraints determining what counts as a recognisable reason for a decision. It employs the theoretical apparatus of Davidson’s project of Radical Interpretation to explore the epistemology of interpretation, interrogating the conditions under which intentional attribution and the provision of reason explanations for behaviour are possible. It is contended that beliefs are intrinsically rational and intersubjective, and that judgements of irrationality are only possible against a background of shared belief between interpreter and observed agent. This view is defended against the objection that rationality is too stringent a constraint on belief.\ud \ud A misconception giving rise to this objection is then diagnosed. Drawing an analogy with Wittgenstein’s rule-following considerations, it is submitted that the constitutive normativity of belief need not be codified in order to exert a genuine constraint on intentional behaviour. Rather, the norms of belief ought to be construed as emerging from shared practice. This indicates that normative judgements are disciplined through expertise and experience, rather than adherence to abstract principles. Finally, the implications of these insights for conceptualising and assessing capacity are considered
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