There are all grades and degrees of "knowledge," and it is more than probable that there is a state of mind which I have heard an astute expert call upon the witness stand "an insane knowledge," and equally obvious that there may be "imperfect" nor "incomplete knowledge," where the victim sees "through a glass darkly." Certainly it seems far from fair to interpret the test of responsibility to cover a condition where the accused may have had a hazy or dream-like realization that his act was technically contrary to the law, and even more dangerous to make it exclude one who was simply unable to "judge calmly and reasonably" of his proposed action, a doctrine which could almost be invoked by any one who committed homicide in a state of anger.
*"General View of the Criminal Law," p.

80.
Ordinarily the word is not defined at all and the befuddled juryman is left to his own devices in determining what significance he shall attach not only to this word but to the test as a whole.
An equally ambiguous term is the word "wrong." The judges made no attempt to define it in 1843, and it has been variously interpreted ever since.

Now it may mean "contrary to the dictates of conscience" or, as it is usually construed, "contrary to the law of the land"-- and exactly what it means may make a great difference to the accused on trial.

If the defendant thinks that God has directed him to kill a wicked man, he may know that such an act will not only be contrary to law, but also in opposition to the moral sense of the community as a whole, and yet he may believe that it is his conscientious duty to take life.

In the case of Hadfield, who deliberately fired at George III in order to be hung, the defendant believed himself to be the Lord Jesus Christ, and that only by so doing could the world be saved.