| Test | Legal standard |
|---|
| M’Naghten (1843) | “Didn’t know what he or she was doing or didn’t know it was wrong” |
| Irresistible impulse (1886) | “Could not control conduct” |
| Durham (1954) | “Criminal act was caused by mental illness” |
| American Legal Institute (ALI; 1962) | “Lacks substantial capacity to appreciate the wrongfulness of the conduct or to control it” [emphasis added] |
| Present federal law (1984 and 1988) | “Lacks capacity to appreciate the wrongfulness of his or her conduct” |
| Source: Meyer & Weaver, 2006, p. 123, which was adapted in part from Morris, 1986. |