ABSTRACT
The practical difficulty in law has always been the articulation of a reliable and stable test for the kind of abnormality or insanity that would, if established, either absolve the defendant from responsibility, or at least reduce the degree of blame. It is disagreement about the ways in which mental disturbance affects personal responsibility that makes the insanity defence or the plea of diminished responsibility controversial. The English scepticism is compatible with the further assumption that serious mental disturbance - which under some classifications would count as insanity - does not necessarily involve the kind of cognitive impairment that would affect the ability to make moral judgements and decisions. A volitional insanity defence, then, should have arisen naturally from the admissibility of partial insanity as a defence. The first and most obvious objection, frequently voiced in Parliament, is that the admission of irresistible impulse would have the effect of increasing the number of insanity defences beyond an acceptable level.
