may be that he did suppose the existence and materiality of some
circumstance, which either did not exist, or which, though existing,
was not material. In such case the act may be said to be misadvised,
with respect to such imagined circumstance: and it may be said
that there has been an erroneous supposition, or a mis-swpposal in
the case." Under the heading of " Cases unmeet for punishment."
Bentham puts " the case of mis-supposal ; where, although he may
know of the tendency the act has to produce that degree of mischief,
he supposes it, though mistakenly, to be attended with some circum-
stance, or set of circumstances, which, if it had been attended with, it
would either not have been productive of that mischief, or have been
productive of such or greater degree of good, as has determined the
legislature in such a case not to make it penal." Apart from the terms
employed by Bentham, this speculative treatment of principle has
been taken to accord with the actual state of English law. Sir John
Salmond, in dealing with mistake of fact (Jurisprudence, 9th ed. (1937),
sec. 147, p. 561), says : - ' In the criminal law, on the other hand, the
matter is otherwise and it is there that the contrast between mistake of
law and mistake of fact finds its true application. Absolute criminal
responsibility for a mistake of fact is quite exceptional." On the
side of history, the development of the doctrine has not received
any full, or perhaps adequate, treatment. For the most part, writers
are content to begin with the decision given in 1639 that an honest
and reasonable belief that the victim was a burglar was a sufficient
justification for homicide, although the belief was in fact mistaken
(RB. v. Levett (1)). This case is mentioned by Sir William Holdsworth,
whose account of the later history of the mental element in crime
will be found in Holdsworth's History of English Law, vol. 8, pp.
443 et seq. Sir James Fitzjames Stephen (History of the Criminal
Law (1883), vol. 2, p. 117), after saying that the effect of ignorance or
mistake as to a particular matter of fact connected with an alleged
offence is a matter which varies according to the definition of