Legal Definitions - substantial-capacity test

The substantial-capacity test, also known as the Model Penal Code test or American Law Institute (ALI) test, is a legal standard used in some jurisdictions to determine if a person can be held criminally responsible for their actions due to a mental illness.

Under this test, a person is not considered criminally responsible for an act if, because of a mental disease or defect, they lacked the significant ability (substantial capacity) to do either of the following:

• Appreciate the criminality of their conduct: This means they could not understand that their actions were wrong or illegal.
• Conform their conduct to the requirements of the law: This means they could not control their behavior and follow the law, even if they knew what they were doing was wrong.

This test is broader than some other insanity defenses because it considers both a person's ability to understand right from wrong (cognitive capacity) and their ability to control their impulses and actions (volitional capacity).

Examples:

• Example 1 (Appreciating Criminality): A person suffering from severe, untreated psychosis experiences vivid hallucinations and delusions that lead them to believe they are acting under divine command to destroy a specific object, which happens to be someone else's valuable property. In this delusional state, they damage the property.

  Explanation: A defense using the substantial-capacity test might argue that due to their severe mental illness, the individual lacked the substantial capacity to appreciate the criminality or wrongfulness of their act. From their distorted reality, they were fulfilling a sacred duty, not committing an act of vandalism, because their mental disease prevented them from understanding the true nature of their actions within societal norms.

• Example 2 (Conforming Conduct): An individual with a diagnosed severe impulse control disorder, exacerbated by a sudden, intense stressor, experiences an overwhelming and uncontrollable urge to physically lash out at a stranger during a minor disagreement. Despite knowing that hitting someone is illegal and wrong, they feel a compulsion so strong that they cannot resist it, leading to an assault.

  Explanation: Here, the substantial-capacity test could be applied by arguing that while the individual might have understood that assaulting someone was wrong (appreciating criminality), their mental disease or defect (the severe impulse control disorder and acute stress response) deprived them of the substantial capacity to conform their conduct to the law. They were unable to control their actions, even if they knew the actions were illegal.

• Example 3 (Combination of Both): A person with a profound intellectual disability, combined with a severe dissociative disorder, is manipulated by another individual into participating in a robbery. Due to their combined mental impairments, they genuinely do not grasp the serious legal consequences or the moral wrongness of the act, nor do they possess the mental fortitude or understanding to resist the coercion effectively.

  Explanation: In this scenario, the substantial-capacity test could be invoked because the individual's severe mental and intellectual impairments might mean they lacked the substantial capacity to appreciate the criminality of the robbery (they didn't truly understand it was a serious crime with severe consequences) and also lacked the substantial capacity to conform their conduct to the law (they couldn't resist the instruction due to their diminished mental faculties and dissociative state). This example highlights how the test can encompass both cognitive and volitional deficits.