Odger's English Common Law

Chapter II.
THE ELEMENTS OF A GRIME.
To constitute a crime there must, as a rule, be both a guilty
mind and a criminal act. The State does not punish a mere
intention, however criminal, unless it is accompanied by some
external criminal act ; nor, speaking generally, is any act
punishable unless it is done with a criminal intention. This
is usually expressed in the maxim, Actus non facit reum nisi
mens sit rea ;
L
it is equally true that mens rea is insufficient
unless it be followed by some criminal act. " The intent and
the act must concur to constitute the crime."
I. Criminal Act or Omission.
In the first place the offender must be guilty of some
criminal conduct. He must do some act which it is a crime
for him to do, or he must omit to do some act which it is a
crime for him not to do. In most cases tbe criminal does
some act ; but the number of crimes of omission has much
increased during the last hundred years. 3
-'
It is, however, only
where there is a legal duty to act that a mere omission to act
is criminal ; thus it is no crime to stand by and let a man
drown.
A bare intent to commit a crime is not indictable ; some
outward act must be superadded to constitute a crime.
" The imagination of the mind to do wrong without au act
done is not punishable in our law." i
It is true that " compassing the King's death " is treason ; but such
" compassing " must be made manifest by some overt act. 5
1 3 lust. 107 ; as to mens rea, see post, p. 112.
2 Per Lord Kenyon, C. J., in Fowler v. Padget (1798), 7 T. E. at p. 514 ; and
see the judgment of Lord Mansaeld, C. J., in B. v. Scofield (1784), Cald. S. C. at
p. 403.
8 See, for instance, the provisions which make it criminal to neglect, abandon or
expose children, ante, p. 106, and post, pp. 310—313.
* Argument, Hales v. Petit (1562), Plowd. 269 a ; and see the judgments of Lord
Mansfield, C. J., and Lord Kenyon, 0. J., cited above.
5 See post, pp. 145, 147.