How did the formulary system make Roman legal procedure more flexible?

The formulary system increased the flexibility of Roman legal procedure by replacing the rigid, oral requirements of the earlier legis actiones with written instructions.12

Under the older legis actiones, parties were required to recite specific, formal words; even a minor error could result in the loss of a case. In contrast, the formulary system allowed the magistrate to delineate the legal issues in a written document—the formula—which was then presented to the judex (judge). This document provided clear, alternative instructions for the judex, such as: "If it appears that the defendant owes the plaintiff 10,000 sesterces, the judex is to condemn the defendant... if it does not so appear, he is to absolve him".12

By formalizing the issues in writing, the magistrate gained greater power to determine whether a case should proceed, allowing the legal process to adapt to increasingly complex disputes while moving away from the extreme technicality of the previous system.12