partial insanity
a borderline condition in which mental impairment is present but is not sufficiently severe to render the individual completely irresponsible for his or her acts. In legal proceedings, a conclusion of partial insanity may arise when there is evidence that a mental disorder was probably a contributing cause to a defendant’s criminal actions or that the disorder rendered the individual incapable of deliberation, premeditation, malice, or another mental state usually requisite for first-degree offenses; in such circumstances, it may lead to conviction for a lesser offense. See also diminished responsibility; insanity; M’Naghten rule.