A more thorough explanation:

American Law Institute Test

The American Law Institute Test, also known as the Substantial-Capacity Test, is a legal standard used in criminal law to determine if a person is not criminally responsible for an act due to a mental disease or defect. According to this test, a person lacks substantial capacity either to appreciate the criminality of the conduct or to conform the conduct to the law. This test combines elements of both the McNaghten rules and the irresistible-impulse test by allowing consideration of both volitional and cognitive weaknesses.

For example, if a person with a mental illness commits a crime but did not understand that their actions were wrong or could not control their behavior due to their illness, they may be found not guilty by reason of insanity under the American Law Institute Test. However, since 1984, many jurisdictions have narrowed the insanity defense and adopted a new test resembling the McNaghten rules, although portions of the substantial-capacity test continue to be used.

Another example could be a person with a severe intellectual disability who commits a crime but does not understand the consequences of their actions. Under the American Law Institute Test, they may be found not criminally responsible for their actions.

These examples illustrate how the American Law Institute Test is used to determine if a person's mental illness or defect affected their ability to understand the criminality of their actions or to conform their behavior to the law.