Justice Scalia theorized that reasonableness review can be only procedural and not substantive. This conclusion flows from the Sixth Amendment requirement that any fact legally necessary to support a sentence must be either admitted by the defendant or found by a jury. If a sentence is upheld as substantively reasonable, it could have been the product of judicial factfinding, even if those facts yielded a sentence within a guidelines range. That holding would, in Scalia's view, violate the rule of "Apprendi v. New Jersey". Since the Sixth Amendment would curtail judicial factfinding in some cases, and Congress intended for a uniform standard of review to apply, there could be no substantive review of sentences for reasonableness.