Odger's English Common Law

126 THE ELEMENTS OF A CRIME.
For the same reason no infant under seven years of age can
commit a crime. The law also presumes that an infant above
seven but under fourteen years is incapable of committing a
crime, for he has not yet acquired sufficient discretion to
know right from wrong. This presumption, however, may
be rebutted (except in the case of rape and offences involving
carnal knowledge) by evidence that the infant knew what
he was doing, and understood the wrongful nature of his
act. 1
„ No lunatic will be punished if he does not know what he is
doing, or does not know that what he is doing is wrong. If
he knows both what he is doing and that he ought not to do
it, he is liable, although his desire to do it may be prompted
by some delusion ; for his motive is, as a rule, immaterial so
far as guilt or innocence is concerned. But he will not be
liable where the delusion is of such a kind that, if the facts
were as he supposed, his act would be justifiable. Again, as
insanity may affect the will as well as the judgment, it is
possible that a crime may be committed under the influence
of some uncontrollable impulse : this, if proved, would be a
defence. But it is very difficult to establish this defence to
the satisfaction of the Court. 2 Mere irresistible impulse to
do wrong affords no exception, if the intellectual faculties
are in such a state that the offender knows he is doing
wrong.
Duress or compulsion is a defence to all save the gravest
crimes. There are two forms of duress— physical and moral
This distinction can best be explained by two instances. If
A. seizes the hand of B., in which there is a knife, and by
physical force compels B. to stabC, B. will not be guilty of
murder, for he cannot help doing what he does ; the stabbing,
indeed, is A.'s act and not B.'s. Here the compulsion is
physical. But if A. threatens to kill or injure B. unless
he stabs C, and B. under such moral compulsion does
stab C, he will be guilty of murder; for he could and
ought to have refused to stab C, although at the risk of his
1 See poet, Book VI:, Chap. II., Infants.
2 See post, Book VI., Chap. III., Lunatics.