Presumption of culpable mental state shifts evidential burden, allowing defence to prove absence of such state. The Act presumes a culpable mental state in prosecutions requiring it, subject to a defence by the accused to prove absence of that mental state; 'culpable mental state' includes intention, motive, knowledge, and belief or reason to believe a fact; a fact is proved only when the court believes it beyond reasonable doubt, not by preponderance of probability.