I. Railway rate theory developed to explain and justify rates not based on cost, 168.— Early analysis an overhead-cost theory, 173.— Terminology, 174.— Development of overhead-cost theory, 178.— Joint-cost explanation, 182.— Criticism of the analogy, 184.— Monopoly explanation, 185.— Grouping of later writers, 186.— The attack on the joint-cost theory, 189.— Back hauls, 197.— Defenders of the joint-cost theory, 199.— Classification of recent writers, 203.— Discrimination not always possible, 206. II. Do preferential rates burden other traffic? 208.— Charging what the traffic will bear and monopoly profits, 214.— Value of service leading to excessive rates, 220.— Arguments for cost of service, 224.— Are cost allocations practicable? 225.— The assumption of unused capacity, 228.— Differential charging will persist, 229.