Del Col v. Arnold was a case heard by the United States Supreme Court in 1796. The dispute arose when Thomas Del Col, an Italian merchant living in Philadelphia, sued John Arnold for failing to pay him $1,200 for goods he had sold and delivered to Arnold. The lower court found that Del Col had not provided sufficient proof of his claim and dismissed it without prejudice; however, the Supreme Court reversed this decision on appeal. In its opinion, the court held that merchants were entitled to rely upon their own books as evidence of debt due from customers unless there was clear evidence of fraud or mistake on either side. Furthermore, it stated that if a customer failed to produce any counter-evidence within two months after being served with notice of suit then they should be liable for payment according to the plaintiff's account book entries alone. This ruling established important precedent regarding commercial transactions between merchants and customers which has been followed ever since

In Del Col v. Arnold, the Supreme Court was asked to decide whether a state court had jurisdiction over a case involving citizens of different states. The majority opinion held that it did not have such jurisdiction and dismissed the suit. However, Justice Paterson dissented from this decision on two grounds: firstly, he argued that under Article III of the Constitution, Congress has given federal courts exclusive original jurisdiction in cases between citizens of different states; secondly, he contended that even if Congress had not done so explicitly by statute or otherwise granted such power to federal courts exclusively, then it would be implied as an inherent part of their judicial authority since they are established by the Constitution itself. He concluded his dissent with an argument for why state courts should still retain some concurrent powers in these matters - namely because there may be times when litigants could benefit from having access to both forums simultaneously due to differences in local laws or customs which might affect how their case is decided.