Page "M'Naghten rules" Paragraph 9

The next major advance occurred in Hadfield's Trial 1800 27 How St. Tr.

765 in which the court decided that a crime committed under some delusion would only be excused if it would have been excusable had the delusion been true.

This would deal with the situation, for example, when the accused imagines he is cutting through a loaf of bread, whereas in fact he is cutting through a person's neck.