The answer is no. Diminished capacity is not recognized as a defense in Illinois. However, you might instead consider whether you were not guilty by reason of insanity or guilty but mentally ill.

In the that recognize diminished capacity, a legally sane defendant may present evidence of mental illness to negate the specific intent required to commit a particular crime. Diminished capacity may be caused by intoxication, trauma or disease.

For example in People v. Frazier, the defendant, an Iraq military veteran, claimed his PTSD prevented him from forming the intent necessary to commit aggravated discharge of a firearm. In that case, the court rejected this defense.

In contrast, under the insanity defense, you may not be criminally responsible for your offense as a result of mental disease or defect where you lack the substantial capacity to appreciate the criminality of your conduct. The terms “mental disease or mental defect” do not include abnormalities manifested only by repeated criminal or otherwise antisocial conduct. In other words, you would not likely have an insanity defense if you were a serial killer without some other form of mental illness.

If you are mentally ill, but not insane, you may still be held criminally responsible for your conduct. This is known as guilty but mentally ill. In this sense, “mentally ill” means you had a substantial disorder of thought, mood or behavior which impaired your judgment, but not to the extent that you were unable to appreciate the wrongfulness of your behavior.

If you have been charged with a crime, contact an experienced criminal law attorney immediately. An attorney can review your case for its best possible defense. Did the police have probable cause to arrest you? Can the state prove all the elements of your offense beyond a reasonable doubt? Even if the police acted lawfully and the evidence against you is overwhelming, an attorney who is respected in the courthouse may be able to negotiate a more favorable plea agreement than you could on your own.

If you have questions about this or another related Illinois criminal or traffic matter, please contact Matt Keenan at 847-568-0160 or email

(Besides Skokie, Matt Keenan also serves the communities of Arlington Heights, Chicago, Deerfield, Des Plaines, Evanston, Glenview, Morton Grove, Mount Prospect, Niles, Northbrook, Park Ridge, Rolling Meadows, Wilmette and Winnetka.)

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