This paper examines the intersection of dementia with the physiological processes and social contexts of old age; assesses the current legal response to problems arising through that intersection; and considers the potentially transformative effect of re-thinking legal response with those contextualised problems in mind. Two distinctive problems are identified: a heightened risk of exploitation, and an increasingly intense need for care coinciding with a decreasing ability to recognise and respond to that need. These problems require a social (rather than medical) response, of which law is an integral part. Several areas of law (including adult guardianship, legislation and common law doctrine relating to health care consent/refusal, and the body of law relating to decision-making about agreements, transactions, and bequests) provide for that response through the medico-legal construct of mental capacity. This legal idea of mental capacity has survived extensive critique, particularly in relation to interpretation and implementation of Article 12 of the Convention on the Rights of Persons With Disabilities. The survival of the mental capacity construct can be attributed to its usefulness as a theoretical mechanism that provides both a justification for over-ruling choice and preference (locating autonomy in the mentally capable decision) and a process for doing so (the mental capacity assessment and determination). This ambit of usefulness is particularly relevant to the problems (arising in the context of dementia in old age) identified in this paper. Both problems engage the public interest, together with the fundamental legal principle of fairness, in ways that call for legal response of some kind. Supported decision-making, as the suggested replacement for mental capacity based legal response, applies awkwardly in these contexts; as far as the individual is concerned, her decision has been made (and she does not need assistance in making one). This paper concludes that the mental capacity construct is problematic both for the reasons identified in the CRPD discourse (in which the experience of dementia in old age has been largely invisible) and because of the complicated intersections between mental capacity, dementia, and old age. The paper concludes by setting out an alternative conceptual basis and framework for legal response, including over-ruling expressed choice and preference, constructed around a principled theory of vulnerability as an alternative to and replacement for the mental capacity construct.
