People v. Roder 33 Cal.3d 491, 189 Cal.Rptr. 501, 658 P.2d 1301 (1983) Roder owned a pawn shop.  He was arrested on suspicion of receiving stolen property, specifically a clarinet. In order to prove the charge, the prosecution had to prove that Roder had knowledge that the property had been stolen. Roder had the clarinet in his pawn shop, so the main issue was whether or not he knew it had been stolen (aka guilty knowledge). At the end of the trial, the Trial Judge gave the jury an instruction that, per California law (Penal Code §496(2)), there was a statutory presumption of guilty knowledge if: The accused was a dealer in secondhand merchandise who had bought the stolen merchandise under circumstances which should have caused him to make a reasonable inquiry about whether the seller had stolen it, but didn't make the inquiry. The Trial Judge further instructed the jury that this was a rebuttable presumption, and it was Roder's responsibility to present evidence that he did not know the clarinet was stolen. Under California law, if Roder didn't present evidence, then they just must presume that he knew it was stolen. The Trial Court found Roder guilty of receiving stolen property.  He appealed. The California Supreme Court reversed. The California Supreme Court looked to Ulster County Court v. Allen (442 U.S. 140 (1979)), and found that a mandatory presumption was unconstitutional because it relieves the prosecution of its burden of proving all elements of the criminal offense beyond a reasonable doubt. Basically, in a criminal case, you can't presume the accused is guilty and make them offer evidence to prove their innocence. The Court looked at the specific wording of the jury instructions and found that it would reasonably be interpreted as relieving the prosecution of its burden of proving every element of the offence beyond a reasonable doubt. The Court issued an order that under FRE 501, the California law should be interpreted as to only authorizing a permissive inference, and not a mandatory presumption. Under the decisions in Allen, and Sandstrom v. Montana (442 U.S. 510(1979)), there are two kinds of presumptions: A permissive inference or presumption, where you tell the jury that they can presume something happened if they want to. This is constitutional because it leaves the jury free to credit or reject the inference and does not shift the burden of proof. A mandatory presumption, where you tell the jury that they must presume that something happened. This is not constitutional unless the facts proved are sufficient to support the inference of guilt beyond a reasonable doubt.