Mental illness may be manifested in the impairment of understanding or of volitional control. Impairment of understanding may be manifested in delusions. Impairment of volitional control is shown when a person is unable to act in accordance with good reasons that he himself accepts. In order for an impairment of understanding or of self-control to exculpate, the offence must be causally connected with the impairment in question. The rationale of exculpation in general, which applies also to the case of mental (...) illness, is that the offence does not indicate a morally bad attitude in the offender. A consequence of this rationale is that Kenny is wrong to hold that no injustice would result from the elimination of the legal defence of diminished responsibility. (shrink)