of the law is no excuse for breaking it. This substantive
principle is sometimes put in the form of a rule of evidence,
that every one is presumed to know the [48] law. It has
accordingly been defended by Austin and others, on the ground of
difficulty of proof. If justice requires the fact to be
ascertained, the difficulty of doing so is no ground for refusing
to try. But every one must feel that ignorance of the law could
never be admitted as an excuse, even if the fact could be proved
by sight and hearing in every case. Furthermore, now that parties
can testify, it may be doubted whether a man's knowledge of the
law is any harder to investigate than many questions which are
gone into. The difficulty, such as it is, would be met by
throwing the burden of proving ignorance on the lawbreaker.

The principle cannot be explained by saying that we are not only
commanded to abstain from certain acts, but also to find out that
we are commanded. For if there were such a second command, it is
very clear that the guilt of failing to obey it would bear no
proportion to that of disobeying the principal command if known,
yet the failure to know would receive the same punishment as the
failure to obey the principal law.

The true explanation of the rule is the same as that which
accounts for the law's indifference to a man's particular
temperament, faculties, and so forth. Public policy sacrifices
the individual to the general good. It is desirable that the
burden of all should be equal, but it is still more desirable to
put an end to robbery and murder. It is no doubt true that there
are many cases in which the criminal could not have known that he
was breaking the law, but to admit the excuse at all would be to