Catechism of the Catholic Church §2411 — excerpt
Contracts are subject to commutative justice which regulates exchanges between persons in accordance with a strict respect for their rights. Commutative justice obliges strictly; it requires safeguarding property rights, paying debts, and fulfilling obligations freely contracted.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.