This dissertation seeks to examine the validity of the justification commonly offered for a coercive (1) psychiatric intervention, namely that the intervention was in the ‘best interests’ of the subject and/or that the subject posed a danger to others. As a first step,it was decided to analyse justifications based on ‘best interests’ [the ‘Stage 1’ argument] separately from those based on dangerousness [the ‘Stage 2’ argument]. Justifications based on both were the focus of the ‘Stage 3’ argument. Legal and philosophical (...) analyses of coercive psychiatric interventions generally regard such interventions as embodying a benign paternalism occasioning slight, if any, ethical concern. Whilst there are some dissenting voices even at the very heart of academic and professional psychiatry, the majority of psychiatrists also appear to share such views. The aim of this dissertation is to show that such a perspective is mistaken and that such interventions raise philosophical and ethical questions of the profoundest importance.(2) The philosophical well-spring of the Stage 1 dissertation argument lay in an observation made by Philippa Foot (3) that the “… right to be let free from unwanted interference” is one of the most fundamental and distinctive rights of persons, a right which takes precedence over any “… action we would dearly like to take for his sake.” This – in conjunction with the recognition that some coercive psychiatric interventions are of a gravity as to result in the personhood of the subject being severely damaged if not destroyed – suggested that the concept of personhood play a central role in the formulation of the dissertation argument. For ease of analysis it was presumed that the term ‘person’ could be defined by a set of necessary and sufficient conditions of which ‘minimum levels of rationality’ and ‘ability to communicate’ were the only conditions relevant to the formulation of justifications for coercive psychiatric interventions. This presumption was explicated into a number of postulates which enabled the construction of a rigorous foundation on which to develop the dissertation argument. This argument then sought to determine whether psychiatric assessments of irrationality were accurate and reliable. In furtherance of this analysis it was necessary to examine the reliability of psychiatric determinations in other areas of claimed expertise namely diagnosis, treatment and assessment of dangerousness. This ‘crossing of the disciplinary threshold’ brought to light the dearth of studies on psychiatric misdiagnosis and iatrogenic harm. A variant of the Precautionary Principle was developed to enable the extent of such harms to be estimated. The not insignificant levels of psychiatric misdiagnosis and iatrogenic harm and erroneous assessments of dangerousness which were thus found are of considerable relevance to any ethical analysis of the justification for coercive psychiatric intervention and serve to undermine simple paternalistic justifications. --- (1)The term ‘coercive’ (rather than ‘non-consensual’) is used to indicate an intervention carried out against the explicit and contemporaneous objections of the subject (2)Not least because the number of individuals detained in Irish psychiatric hospitals is of a comparable order of magnitude to the number detained in Irish prisons subsequent to a criminal conviction (3)See Foot (1977), p.102. (shrink)