In short, I look on delusion ....

and insanity to be almost, if not altogether, convertible terms."* * Dew vs.

Clark.
This in a certain broad sense, probably not intended by the judge who made the statement, is nearly true, but, unfortunately, is not entirely so.
The dense ignorance surrounding mental disease and the barbarous treatment of the insane within a century are facts familiar to everybody.

Lunatics were supposed to be afflicted with demons or devils which took possession of them as retribution for their sins, and in addition to the hopelessly or maniacally insane, medical science recognized only a so-called "partial" or delusionary insanity.

Today it would be regarded about as comprehensive to relate all mental diseases to the old-fashioned "delusion" as to regard as insane only those who frothed at the mouth.
But the particular individual out of whose case in 1843 arose the rule that is in 1908 applied to all defendants indiscriminately was the victim of a clearly defined insane delusion, and the four questions answered by the judges of England relate only to persons who are "afflicted with insane delusions in respect to one or more particular subjects or persons." Nothing is said about insane persons without delusions, or about persons with general delusions, and the judges limit their answers even further by making them apply "to those persons who labor under such partial delusion only and are not in other respects insane"-- a medical impossibility.
Modern authorities agree that a man cannot have insane delusions and not be in other respects insane, for it is mental derangement which is the cause of the delusion.
In the first place, therefore, a fundamental conception of the judges in answering the questions was probably fallacious, and in the second, although the test they offered was distinctly limited to persons "afflicted with insane delusions," it has ever since been applied to all insane persons irrespective of their symptoms.
Finally, whether the judges knew anything about insanity or not, and whether in their answers they weighed their words very carefully or not, the test as they laid it down is by no means clear from a medical or even legal point of view.
Was the accused laboring under such a defect of reason as not to know the nature and quality of the act he was doing, or not to know that it was wrong?
What did these judges mean by know?
What does the reader mean by know?
What does the ordinary juryman mean by it?
We are left in doubt as to whether the word should be given, as justice Stephens contended it should be, a very broad and liberal interpretation such as "able to judge calmly and reasonably of the moral or legal character of a proposed action,"* or a limited and qualified one.