This article is concerned with the situation when, at the end of the prosecution or defence case, in a criminal trial, it emerges that the accused is not guilty as charged but that he has certainly committed a criminal offence of a similar type to the offence charged. To take four examples: A is charged with murder, malice aforethought is not proved, yet A has committed manslaughter. Secondly, A is charged with murder or manslaughter and the prosecution fails to prove that the death resulted from A's actions. A has, however, committed the offence of unlawfully doing grievous harm or assault occasioning actual bodily harm. Next, the charge is attempted murder and it fails because the prosecution cannot prove the stringent mental element (an actual, not just constructive, intention to kill), yet A has committed the offence of unlawfully doing grievous harm or of assault occasioning actual bodily harm. Finally, A is accused of theft but since the complainant consented to the taking he is again not guilty of the offence charged, but has committed the crime of obtaining by false pretences. This type of situation may arise because the evidence does not go as anticipated by the prosecution, or because the prosecutor trips up over some subtle legal point like the difference between theft and obtaining by false pretences. Without the exceptional principles which form the subject of this article, the upshot would be that (after the expense of a trial) the accused would go free although he had clearly committed a crime.