Psychopaths and insanity: Law, ethics, cognitive neuroscience and criminal responsibility

  • Simon Barnes

Student thesis: Phd


In many jurisdictions, including England and Wales, psychopaths are unable to succeed with an insanity defence. This has been influenced by a legal view of psychopathy as a condition characterised by a reduced ability to comply with the law, which is otherwise fully understood. Evidence from cognitive neuroscience, however, may potentially challenge this traditional legal conception of psychopathy. In this regard it has already been suggested, based partly on scientific evidence, that it may be appropriate for at least some psychopaths to succeed with an insanity defence where they can be shown to lack moral competence.In this thesis, I critically examine this possibility. I first examine the insanity defence in English law, showing how psychopaths have effectively been excluded from the defence by judicial interpretation of the insanity defence criteria. Consequently, if psychopaths lacking moral competence were to be identified, reform (or reinterpretation) of the defence would be required. I then present philosophical arguments in favour of the case that some psychopaths should gain access to an insanity defence, before clarifying which psychopaths ought potentially to succeed, and which criminal offences ought potentially to be relevant, for the purposes of a reformed or reinterpreted defence. In order to clarify which psychopaths are relevant psychopaths (RPs), it is necessary to go beyond existing scientific evidence. It is argued, based on emerging neuroscientific findings and current research techniques, that while it is not currently possible to identify RPs, it may be possible in the future. Even if it this becomes possible, however, the philosophical case for access to an insanity defence remains deeply problematic. Although RPs may lack moral competence, for example, they may nevertheless possess other capacities relevant to criminal responsibility. After closer examination, it is argued that the case for access to an insanity defence may be best viewed as a case for mitigation rather than exculpation. I conclude by considering some of the implications of this analysis in an English legal context, should it become possible to identify RPs. Of particular relevance is the possibility that RPs may be at high risk of causing serious harm to others. This illuminates important possible relationships between responsibility and risk, and diagnostic advancements and risk assessment, in this area. There are also broader implications for the management of psychopaths in the future, given that greater scientific understanding may lead to enhanced predictive abilities that could tempt policymakers towards more radical strategies.This thesis contributes to an ongoing debate about the role that cognitive neuroscience may play in decisions about the criminal responsibility of psychopaths. My main contribution is to clarify how psychopaths lacking moral competence may be identified in the future, and relate this neuroscientific discourse to arguments for providing these persons with access to an insanity defence. It is argued, however, by reference to legal, policy, scientific and philosophical considerations, that the risk such persons would pose, rather than their capacity for criminal responsibility per se, may have significant legal and policy implications in England and Wales in the future.
Date of Award31 Dec 2014
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorSoren Holm (Supervisor), Simona Giordano (Supervisor) & Neil Allen (Supervisor)


  • criminal law
  • mental health law
  • ethics
  • neuroscience
  • criminal responsibility
  • insanity defence
  • psychopathy

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