in a per curiam decision, the supreme court vacated the ruling of the massachusetts supreme judicial court. citing "district of columbia v. heller" and "mcdonald v. city of chicago", the court began its opinion by stating that "the second amendment extends, prima facie, to all instruments that constitute bearable arms, even those that were not in existence at the time of the founding" and that "the second amendment right is fully applicable to the states". the court then identified three reasons why the massachusetts court's opinion contradicted prior rulings by the united states supreme court. first, the massachusetts court said that stun guns could be banned because they "were not in common use at the time of the second amendment’s enactment", but the supreme court noted that this contradicted "heller"'s conclusion that second amendment protects "arms ... that were not in existence at the time of the founding”. second, the massachusetts court said that stun guns were "dangerous per se at common law and unusual" because they were "a thoroughly modern invention", but the supreme court held that this was also inconsistent with "heller". third, the massachusetts court said that stun guns could be banned because they were not "readily adaptable to use in the military", but the supreme court held that "heller" rejected the argument that "only those weapons useful in warfare" were protected by the second amendment.