Treatise on Law

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Treatise on Law is St. Thomas Aquinas' major work of legal philosophy. It forms questions 90-108 of the Prima Secundæ ("First [Part] of the Second [Part]") of the Summa Theologiæ,[1] Aquinas' masterwork of Scholastic philosophical theology. Along with Aristotelianism, it forms the basis for the legal theory of Catholic canon law.[2]

Aquinas' notion of law[edit]

Question 90 culminates in Aquinas' definition of law:[3]

However, strictly speaking, this is a definition of human law.[5] The term "law" as used by Aquinas is equivocal, meaning that the term does not have exactly the same meaning in every case.[6] For Aquinas, law is an "analogous term"—a term with meanings regulated by a chief meaning.[7] Human law is the primary meaning of "law" which is applied analogously to the other meanings.[8]

"an ordinance of reason"[edit]

For Aquinas, law must be reasonable;[9] it is based in reason and not in the mere will of the legislator, as "the Jurist" says.[10][11]

"for the common good"[edit]

The goal or end of law is the good of the given community upon which it is binding.[12]

Kinds of law[edit]

Natural law[edit]

Human law[edit]

For Aquinas, human law is only valid if it conforms to natural law. If a law is unjust, then it is not actually a law, but is a "perversion of law".[13][14]



Q. 90: Of the Essence of Law
Q. 91: Of the Various Kinds of Law
Q. 92: Of the Effects of Law


Q. 93: Of the Eternal Law
Q. 94: Of the Natural Law
Q. 95: Of Human Law
Q. 96: Of the Power of Human Law
Q. 97: Of Change in Laws
Q. 98: Of the Old Law
Q. 99: Of the Precepts of the Old Law
Q. 100: Of the Moral Precepts of the Old Law
Q. 101: Of the Ceremonial Precepts in Themselves
Q. 102: Of the Causes of the Ceremonial Precepts
Q. 103: Of the Duration of the Ceremonial Precepts
Q. 104: Of the Judicial Precepts
Q. 105: Of the Reason for the Judicial Precepts
Q. 106: Of the Law of the Gospel, Called the New Law, Considered in Itself
Q. 107: Of the New Law as Compared with the Old
Q. 108: Of Those Things That Are Contained in the New Law


    James Fieser
    Journal of Philosophical Research, 1992, Vol. 17, pp. 147-164.
    accessed Dec-17-2013
  2. ^ Dr. Edward N. Peters,, accessed Dec-17-2013
  3. ^ Gateway Edition, pg. ix
  4. ^, accessed Dec-19-2013
  5. ^ Gateway Edition, pg. viii
  6. ^ Gateway Edition, pg. vii
  7. ^ Gateway Edition, pg. vi
  8. ^ Gateway Edition, pg. x
  9. ^ Law of Christ I, pg. 236
  10. ^ Gateway Edition, pg. 2 (Summa, Ia-IIæ, Q.90, A.1, Obj.3)
  11. ^ J. Budziszewski, Commentary on Treatise on Law, accessed Dec-19-2013
  12. ^ Law of Christ I, pg. 236
  13. ^ Summa I-II, q95, a2, 'dicendum quod
  14. ^ Internet Encyclopedia of Philosophy, "Natural Law", accessed Dec-20-2013
  15. ^, accessed Dec-17-2013


St. Thomas Aquinas, Treatise on Law (Summa Theologica, Questions 90-97)
With a New Introduction by Ralph McInerny, University of Notre Dame
Gateway Editions, Regnery Publishing, Inc.
Washington, D.C.
©1956; 2001 printing

Bernard Häring, C.SS.R, The Law of Christ, Vol. I
Translated by Edwin G. Kaiser, C.PP.S.
The Newman Press
Westminster, Maryland
©1961, Second Printing November 1961

See also[edit]