The ubiquitous use of computers has revolutionized both legal practice and commercial activity. Agreements that have been implemented on the basis of oral or hand-squeezing, at one end of the spectrum or only after lengthy negotiations and the exchange of draft documents, which had to be drawn up from scratch at the other stage, are now often determined by writings developed to a minimum of effort and based on a computerized form. , which is used by a contracting party. , or his lawyers, in some previous agreements. The simple « bulking and copying » of similar contracts and instruments, and the often equivalent reduction in the attention paid to a particular agreement at the design stage, increases the risk of misunderstanding between the parties to these agreements when the time comes to implement them. When disputes arise, threshold questions are often the same for the parties, their lawyer and the court: what are the full terms of the parties` agreement? What was the intention of the parties to conclude the agreement? And how can we prove (or defy) these terms and intentions? The rule also implies that if there is other evidence besides the four corners of the document, it cannot be used in court if it directly opposes the information in the four corners of the document. External evidence includes any communication between the parties prior to the signing of the contract, previous versions of the projects and others. Because of the rule of the four corners in the United States, it is important to include all the information desired in the treaty itself. The contract must best demonstrate the clear and defined intent of the parties. If we did not do that or rely on promises outside the treaty, it would be very difficult to implement them. Overall, a judge will not seek to uncover hidden meanings or obscure definitions. Instead, they use the ordinary and simple meaning of words and clauses to determine how certain statements fit into the agreement as a whole.
The doctrine of the four corners resembles the Parol rule of evidence, which prohibits a contractor from providing separate evidence of the contract that would fundamentally alter the intended understanding as set out in the contract.