The "Durham Rule"

The Durham Rule, a version of which was originally adopted in New Hampshire in 1871, was embraced by the Circuit Court of Appeals for the District of Columbia in the 1954 case of Durham v. United States. The Durham Rule, sometimes referred to as the "product test," provides that the defendant is not "criminally responsible if his unlawful act is the product of a mental disease or defect."

The Durham Rule was originally seen as a way of simplifying the M'Naghten Rule and the Irresistible Impulse Test by making insanity and its relation to the crime a matter of objective diagnosis. Nevertheless, such a diagnosis proved to be more difficult to prove in practice than in theory. The test was criticized because the Circuit Court has provided no real definitions of "product," "mental disease," or "defect." Because the Durham Rule proved very difficult to apply, the Circuit Court abandoned it in 1972. Currently, only the state of New Hampshire still uses the Durham Rule as a way to define insanity.