Hugo Black,
Capitol Greyhound Lines v. Brice…
“ Systems of taxation need not achieve the ideal. But the fact that the Constitution does not demand pure reason and is satisfied by practical reason does not justify unreason. Though a State may levy a tax based upon the privilege granted, as distinguished from its exercise, this does not sanction a tax the measure of which has no reasonable relation to the privilege. Reason precludes the notion that a tax for a privilege may disregard the absence of a nexus between privilege and tax. Our decisions reflect that reason. A State naturally may deem factors of size or weight to be relevant. ”
