Catechism of the Catholic Church
2408 The seventh commandment forbids theft, that is, usurping another's property against the reasonable will of the owner. There is no theft if consent can be presumed or if refusal is contrary to reason and the universal destination of goods. This is the case in obvious and urgent necessity when the only way to provide for immediate, essential needs (food, shelter, clothing . . .) is to put at one's disposal and use the property of others. 191
2409 Even if it does not contradict the provisions of civil law, any form of unjustly taking and keeping the property of others is against the seventh commandment: thus, deliberate retention of goods lent or of objects lost; business fraud; paying unjust wages; forcing up prices by taking advantage of the ignorance or hardship of another. 192
The following are also morally illicit: speculation in which one contrives to manipulate the price of goods artificially in order to gain an advantage to the detriment of others; corruption in which one influences the judgment of those who must make decisions according to law; appropriation and use for private purposes of the common goods of an enterprise; work poorly done; tax evasion; forgery of checks and invoices; excessive expenses and waste. Willfully damaging private or public property is contrary to the moral law and requires reparation.
2410 Promises must be kept and contracts strictly observed to the extent that the commitments made in them are morally just. A significant part of economic and social life depends on the honoring of contracts between physical or moral persons - commercial contracts of purchase or sale, rental or labor contracts. All contracts must be agreed to and executed in good faith.
2411 Contracts are subject to commutative justice which regulates exchanges between persons and between institutions 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. Without commutative justice, no other form of justice is possible.
One distinguishes commutative justice from legal justice which concerns what the citizen owes in fairness to the community, and from distributive justice which regulates what the community owes its citizens in proportion to their contributions and needs.
2412 In virtue of commutative justice, reparation for injustice committed requires the restitution of stolen goods to their owner:
Jesus blesses Zacchaeus for his pledge: "If I have defrauded anyone of anything, I restore it fourfold." 193 Those who, directly or indirectly, have taken possession of the goods of another, are obliged to make restitution of them, or to return the equivalent in kind or in money, if the goods have disappeared, as well as the profit or advantages their owner would have legitimately obtained from them. Likewise, all who in some manner have taken part in a theft or who have knowingly benefited from it - for example, those who ordered it, assisted in it, or received the stolen goods - are obliged to make restitution in proportion to their responsibility and to their share of what was stolen.
2413 Games of chance (card games, etc.) or wagers are not in themselves contrary to justice. They become morally unacceptable when they deprive someone of what is necessary to provide for his needs and those of others. The passion for gambling risks becoming an enslavement. Unfair wagers and cheating at games constitute grave matter, unless the damage inflicted is so slight that the one who suffers it cannot reasonably consider it significant.
2414 The seventh commandment forbids acts or enterprises that for any reason - selfish or ideological, commercial, or totalitarian - lead to the enslavement of human beings, to their being bought, sold and exchanged like merchandise, in disregard for their personal dignity. It is a sin against the dignity of persons and their fundamental rights to reduce them by violence to their productive value or to a source of profit. St. Paul directed a Christian master to treat his Christian slave "no longer as a slave but more than a slave, as a beloved brother, . . . both in the flesh and in the Lord." 194
English Translation of the Cathechism of the Catholic Church for the United States of America © 1997, United States Catholic Conference, Inc.