In the law of evidence, a presumption of a particular fact can be made without the aid of proof in some situations. The types of presumption include a rebuttable discretionary presumption, a rebuttable mandatory presumption, and an irrebuttable or conclusive presumption. The invocation of a presumption shifts the burden of proof from one party to the opposing party in a court trial. Presumptions are sometimes categorized into two types: presumptions without basic facts, and presumptions with basic facts. In the United States, mandatory presumptions are impermissible in criminal cases, but permissible presumptions are allowed.