Introduction

The M'Naghten Insanity Test

Introduction

In 1843 Daniel M'Naghten shot and killed Edward Drummond, the private secretary to Prime Minister Sir Robert Peel. M'Naghten believed that Peel was heading a conspiracy to persecute and kill him, and he fired at Drummond only because he mistook the secretary for his employer.¹ The defense put on extensive expert and lay testimony that delusions had taken hold of M'Naghten, and the jury returned a verdict of not guilty on the ground of insanity.² The public reaction was sharp. The press charged that the defense left madmen free to kill, and Queen Victoria, herself the target of three recent assassination attempts, shared the alarm.³ The House of Lords debated the verdict and put five questions to the judges of England about when insanity excuses crime. Their answers were appended to the report of the case and are treated as part of the decision.⁴ The judges were stating the law as they understood it, and right-wrong language had appeared in earlier cases, yet the precise standard had not been settled before roughly 1800 and was still being refined after that.⁵

The passage from those answers that became famous required that “at the time of the committing of the act, the party accused was laboring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing, or if he did know it that he did not know he was doing what was wrong.”⁶ In modern terms, a defendant is entitled to an acquittal under the traditional M'Naghten rule if he proves a disease of the mind that caused a defect in his reasoning, and that as a result, at the time of the charged conduct, he lacked the capacity either to understand the nature and quality of his actions or to know that they were wrong.⁷ The 1843 formulation made cognitive incapacity and moral incapacity two stand-alone grounds, so proof of either one satisfies the final element.⁸ Because the second ground asks whether the defendant knew right from wrong, the same rule appears under the name right-and-wrong test and under the spellings M'Naughten and McNaghten, all of which an exam may use.⁹ It is the predominant American approach, applied in the federal courts and in a large share of the states in some form.¹⁰

Two framing points govern everything that follows. The first is that “insanity” here is a legal category, and a psychiatric diagnosis does not answer the question. The word carries different tests when the issue is competence to stand trial, capacity to make a will, or commitment, and a definition built for one of those purposes does not transfer to another.¹¹ The criminal defense exists to sort out who is an appropriate subject for criminal punishment, which is why a successful defense usually ends in commitment to a mental institution rather than release.¹² The second point is that the test is cognitive. It asks what the defendant was capable of knowing when he acted; how ill he was, and whether he could resist the impulse, do not enter the inquiry. A defendant who compulsively shoplifts jewelry while fully aware that the conduct is wrong and illegal therefore fails the test, however little control he had.¹³ The reasoning is that a person who knows the conduct is wrong and does it anyway is at least somewhat blameworthy, while a person who lacks that knowledge is not blameworthy at all.¹⁴ Students most often misapply the rule at two edges: the defendant who believes his act was morally right, which turns on whether “wrong” means legally or morally wrong, and the defendant who could not control himself. This chapter takes up both after working through the elements, the way delusions operate within the test, and the rules on proof and on the states' constitutional freedom to define the defense, and it begins by taking the elements apart one at a time.¹⁵