People v. Burton 6 Cal.3d 375, 491 P.2d 793 (1971) Burton was committing an armed robbery. He ended up killing someone. He was arrested and charged with murder. FYI armed robbery includes as assault with a deadly weapon as a necessary element of the crime. At Trial, the Judge instructed the jury that they could find Burton guilty of first-degree murder if they found that the death happened as a result of the robbery, even if that death was unintentional (aka felony murder). Normally first-degree murder required premeditation and deliberation, but a defendant can be culpable of even an unintentional murder if it occurs during the commission of a felony. The Trial Court found Burton guilty of first-degree murder. He appealed. Burton argued that it was unfair to find him guilty of felony murder when the underlying felony was robbery, because robbery is an inherently dangerous felony. Since robbery is a violent crime that often results in people getting hurt, there are severe criminal penalties for robbery. To add extra penalties for the death is a sort of double-jeopardy. That's known as the merger doctrine. The California Supreme Court affirmed the jury instruction. The California Supreme Court found that, according to Burton's logic, felony murder would be inapplicable in all situations where someone was committing a crime with a deadly weapon. The Court rejected that notion as too broad. The Court differentiated crimes where the intent is to hurt someone (e.g. assault), from crimes where the intent is to do something else (e.g. get their money). The Court found that in cases where the purpose of the crime was the infliction of bodily injury, felony murder should not be considered separately. However, in cases where the main purpose of the crime was not the infliction of bodily injury (like robbery), then an unintentional death can result in a felony murder charge. The merger doctrine says that certain violent felonies already include the possibility of a killing in their definitions and sentencing guidelines. Therefore, it is unfair to use them as the underlying (aka predicate) felony for a felony murder charge. However, the merger rule is generally limited to felonies that are not 'independent' of the killing. Basically, that's just assault.