Plausible subjective experience versus fallible corroborative evidence: The formulation of insanity in Nigerian criminal courts.

Insanity as a defence against criminal conduct has been known since antiquity. Going through significant reformulations across centuries, different jurisdictions across the globe, including Nigeria, have come to adopt various strains of the insanity defence, with the presence of mental disorder being the causative mechanism of the crime as their central theme. A critical ingredient in the Nigerian insanity plea is the presence of 'mental disease' or 'natural mental infirmity' as the basis for the lack of capacity in certain cognitive and behavioural domains resulting in the offence.