had no moral
excuse for transgressing it. Governments see that if ignorance of the
law were allowed to excuse a man for any act whatever, it must excuse
him for transgressing all statutes whatsoever, which he himself thinks
inconsistent with his rights and liberties. But such a doctrine would of
course be inconsistent with the maintenance of arbitrary power by the
government; and hence governments will not allow the plea, although they
will not confess their true reasons for disallowing it.

The only reasons, (if they deserve the name of reasons), that I ever
knew given for the doctrine that ignorance of the law excuses no one,
are these:

1. "The reason for the maxim is that of necessity. It prevails, 'not
that all men know the law, but because it is an excuse which every
man will make, and no man can tell how to confute him.'--_Selden_,
(as quoted in the 2d edition of _Starkie on Slander_, Prelim. Disc.,
p. 140, note.)"--_Law Magazine_, (_London_,) vol. 27, p. 97.

This reason impliedly admits that ignorance of the law is,
_intrinsically_, an ample and sufficient excuse for a crime; and that
the excuse ought to be allowed, if the fact of ignorance could but be
ascertained. But it asserts that this fact is incapable of being
ascertained, and that therefore there is a necessity for punishing the
ignorant and the knowing--that is, the innocent and the guilty--without
discrimination.

This reason is worthy of the doctrine it is used to uphold; as if a plea
of ignorance, any more than any other plea, must necessarily be believed
simply because it is urged; and as if it were not a common and every-day
practice of courts and juries, in both civil and criminal cases, to
determine the mental capacity of individuals; as, for example, to
determine whether they are of sufficient mental capacity to make
reasonable contracts; whether they are lunatic; whether they are
_compotes mentis_, "of sound mind and memory," &c. &c. And there is
obviously no more difficulty in a jury's determining whether an accused
person knew the law in a criminal case, than there is in determining any
of these other questions that are continually determined in regard to a
man's mental capacity. For the question to be settled by the jury is not
whether the accused person knew the particular _penalty_ attached to his
act, (for at common law no one knew what penalty a _jury_ would attach
to an offence,) but whether he knew that his act was