Why did medieval Roman-canonical law require testimony from two or more suitable witnesses?

Medieval Roman-canonical law required the testimony of two or more suitable witnesses because it operated under a formal, hierarchical theory of evidence. Influenced by scholastic philosophy, this legal system assumed that all aspects of life could be organized through a system of abstract, a priori regulations.1

Within this framework, the law did not allow judges to exercise personal discretion; instead, they were required to be convinced once a designated number of witnesses had testified concordantly. This requirement for two or more witnesses was considered "full proof," whereas a single witness was generally insufficient to prove a matter. Because the law was based on the concept of the inequality of persons, not every individual was deemed a suitable witness.12

This rigid, formalistic approach was designed to eliminate nonrational evidence from the courts, though it often prioritized the creation of "formal truths" over the reality of the facts.1