The practice of the law often does not conform to its principles. When M'Naghten was tried, insanity was defined by the Wild Beast test - to be NGRI, a person's understanding had to be reduced to that of a 14-year-old. Although M'Naghten's understanding exceeded this standard, the jury found him NGRI because they accepted Stephen's claim that he was so much in the grip of his delusions that he could not stop himself acting on them. The jury were instructed to follow a cognitive test of insanity but instead used a volitional one. Similarly, the jury found Hadfield NGRI using a more liberal cognitive test than the current Wild Beast test.