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Summa Theologica: Treatise on Law

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Summa Theologica: Treatise on Law

The Treatise on Law is Questions 90–108 of the Prima Secundae of Thomas Aquinas’s Summa Theologica (c. 1270) — the most systematic statement of natural law in the Western tradition, and the bridge from classical (Aristotelian and Ciceronian) natural justice to the modern rights tradition.

The Definition and the Fourfold Scheme

Aquinas defines law precisely (Q. 90): “an ordinance of reason for the common good, made by him who has care of the community, and promulgated.” Each clause does work — law is an act of reason (not mere will), aimed at the common good, issued by legitimate authority, and promulgated.

He then distinguishes four kinds of law (QQ. 91–93):

  • Eternal law — God’s rational governance of the whole created order.
  • Natural law — “the rational creature’s participation of the eternal law,” accessible to reason. Its first, self-evident precept (Q. 94) is that “good is to be done and pursued, and evil is to be avoided,” from which all other natural precepts follow (preservation of life, family, knowledge of truth, life in society).
  • Human (positive) law — the particular determinations that human legislators derive from natural law for their communities (QQ. 95–97).
  • Divine law — what is revealed (the Old and New Law, QQ. 98–108), exceeding what reason alone discovers.

Unjust Law Is No Law

The Treatise’s most quoted thesis for the rights tradition is that human law has the force of law only so far as it derives from natural law; a positive enactment that conflicts with natural law “is no longer a law but a perversion of law” (lex iniusta non est lex). This is the precise claim legal positivism later denies — and the claim that lets natural-law thinkers judge a formally valid statute unjust and even non-binding.

Place in This Wiki

Aquinas synthesizes Aristotle (“the Philosopher,” cited on nearly every page) and the Ciceronian / Roman-law vocabulary of natural reason. His “reason for the common good” framing and the unjust-law thesis pass to Grotius and the Late Scholastics, and onward to Locke. The wiki uses Aquinas as the medieval pillar of the lineage, not as a libertarian: his “common good” and his comfort with coercive human law are real differences from the rights-first moderns.

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