Moral insanity referred to a type of mental disorder consisting of abnormal emotions and behaviours in the apparent absence of intellectual impairments, delusions, or hallucinations.
[6] The term 'moral', at that time and taken originally from French, could mean the affective, or interior depth of an individual rather than necessarily a reference to their ethics.
[7] The term 'moral insanity' had been used earlier by Thomas Arnold (physician) and Benjamin Rush in referring to what they saw as a result of madness – a disruption or perversion of the emotions or moral sense.
The other three types involved increasing degrees of intellectual abnormality: a partial derangement that was limited to certain trains of thought; a full mania, by which was meant 'raving madness' regardless of topic; and lastly, a breakdown of any connections between ideas, referred to as incoherence or dementia.
Prichard considered that some early nosologists, namely Sauvages, Sagar and Linnaeus, had distinguished between medical conditions with hallucinations and those involving depraved appetites or feelings.
But he credits Pinel as the first in psychiatry to clearly distinguish madness without delerium, in opposition to Locke's widely accepted axiom that insanity always stemmed from faulty intellectual connections or mistaken perceptions.
The latter term had been introduced by the physician Esquirol, who had succeeded Pinel, to refer to a form of insanity where there is a fixation or excess in only one area.
However, he also linked moral insanity to a debasement of the more refined emotions, which he in turn saw as more associated with the affluent classes, such that a person still knew right from wrong but became unable to conduct themselves "with decency and propriety in the business of life".
Prichard was also concerned to challenge the development of phrenology, which attempted to localise aspects of the mind and personality to particular areas of the brain, as assessed by the size of bumps in the skull.
[16] The context leading to the conceptualization of this diagnostic category was undoubtedly borne out of the frustration of alienists (the term is approximately equivalent to the modern day one of psychiatrist) by the definition of madness provided by John Locke in which delusional symptoms were required.
In legal trials this definition had proved to be a great source of embarrassment to alienists because unless delusional symptoms could be clearly shown judges would not consider a plea of insanity.
[19] Several writers have sounded caution over the notion that the diagnostic category of moral insanity was a direct forerunner of psychopathic disorder.
The diagnosis was meant to imply a congenital disorder, and to be made without moral judgement, though Koch has been described as deeply rooted in a Christian faith.