Common Law and Roman Law: The Same Case under Two Reasons

By Glênio Sabbad Guedes (Lawyer in Brazil)

“Non ex regula ius sumatur, sed ex iure quod est regula fiat.”(Paulus, Digest 50.17.1)

“The life of the law has not been logic; it has been experience.”(Oliver Wendell Holmes Jr., The Common Law, 1881)*

At the dawn of every legal civilization, there is a familiar scene: a man seeking justice, another resisting it, and a third — the jurist or the judge — trying to decide without breaking the fragile balance of the world. This was true in ancient Rome, as it was centuries later in England: both discovered law through the experience of cases, not through the abstraction of codes.

Ius and Common Law are not foreign languages to each other. They are two dialects of the same intellectual tradition: a jurisprudence born of experience, analogy, and prudence. In her remarkable work La giurisprudenza nel sistema delle fonti del diritto romano (2nd ed., Giappichelli, Torino), especially Chapter IV — Il metodo casistico della giurisprudenza classica — Letizia Vacca reveals that the Roman jurist was not a legislator, but an interpreter; not a creator of laws, but a discoverer of justice hidden within human affairs.

Vacca shows that Labeo, Africano, and Julian did not seek rules but reasons. They compared cases, distinguished nuances, and extracted from each situation a ratio iuris — not definitive, but probable, open, and revisable. Their task was to keep the legal order in harmony with equity, adjusting norms to the pulse of life. Hence aequitas was not indulgence, but a technical instrument of rational correction, the meeting point between fairness and public utility.

In medieval England, the judges of the King’s Bench and Common Pleas practiced something similar. The precedent was not a chain but a memory — a mode of prudential reasoning. Lord Coke would later write that “the common law is nothing else but reason.” The judge did not invent law; he found it within the coherence of earlier decisions, just as the Roman prudentes found it in the customs and reason of their predecessors. Both understood that justice does not live in the letter of the law, but in the force of the argument.

Yet there are essential differences.Rome built an authority of prudence — that of the iuris prudentes, who advised the praetor; England built an institutional authority — that of the binding precedent. The first rested on virtue and experience; the second on stability and predictability. The Roman system valued aequitas as a measure of justice; the English one, consistency as a safeguard of legitimacy. But both share the same conviction: law is a form of practical reason, not a collection of commands.

When Labeo introduced his aequitas interpretativa and Julian organized the Edictum perpetuum, Roman law underwent a quiet revolution: it moved from ritual to argument, from oracular formulas to dialectical reasoning. Centuries later, in seventeenth-century England, the Court of Chancery would perform a similar transformation through the rise of equity, tempering the rigidity of common law. In both cases, equity became the rational bridge between law and life, a device that keeps justice alive within institutions.

The jurist and the judge, the Roman and the Englishman, share the same intellectual gesture: to treat the case as a mirror of justice itself. The Roman searches for the ratio aequitatis; the English judge seeks the ratio decidendi. Both turn experience into principle and principle back into experience. That is why, as Vacca concludes, only the analysis of “similar situations” allows one to verify or modify principles — because law evolves by analogy, by correction, and by fidelity to human practice.

Thus Rome and Westminster, though divided by centuries and languages, converge in the same intuition: law lives because it argues. The dialogue between case and principle, between prudence and rule, is the heartbeat of the Western legal mind. And perhaps, if one day all codes were to vanish, it would still be enough for a single person to reason prudently for justice to exist again.

Selected Bibliography

• VACCA, Letizia. La giurisprudenza nel sistema delle fonti del diritto romano. 2ª edizione riveduta ed ampliata. Torino: Giappichelli, 1988. (Chapter IV: Il metodo casistico della giurisprudenza classica).

• HOLMES Jr., Oliver Wendell. The Common Law. Boston: Little, Brown and Company, 1881.

• VILLEY, Michel. La formation de la pensée juridique moderne. Paris: Presses Universitaires de France, 1968.

• GROSSI, Paolo. Mitologie giuridiche della modernità. Milano: Giuffrè, 2001.

• MACCORMICK, Neil. Legal Reasoning and Legal Theory. Oxford: Clarendon Press, 1978.

• PERELMAN, Chaïm. Logique juridique. Nouvelle rhétorique. Paris: Dalloz, 1976.

• RICOEUR, Paul. Le juste. Paris: Éditions Esprit, 1995.