Saint Thomas Aquinas is often considered the greatest Doctor of the Church and the towering mind of medieval society. In 1879, Pope Leo XIII devoted an encyclical to restoring the study of Thomism in Christian philosophy:
We exhort you, venerable brethren, in all earnestness to restore the golden wisdom of St. Thomas, and to spread it far and wide for the defense and beauty of the Catholic faith, for the good of society, and for the advantage of all the sciences… But, lest the false for the true or the corrupt for the pure be drunk in, be ye watchful that the doctrine of Thomas be drawn from his own fountains… be careful to guard the minds of youth from those which are said to flow thence, but in reality are gathered from strange and unwholesome streams.Aeterni Patris § 31
Tragically, Pope Leo’s warning against misreadings and outright lies about the doctrines of Thomas remains relevant. Today, many heretical but well-funded “Whig Thomists” spread the error that St. Thomas’s economic principles are in harmony with capitalism. We aim to correct these ridiculous falsehoods not by offering cherry-picked quotations and interpretations, but by drawing the doctrine of Thomas “from his own fountains.” Below, we have compiled a complete list of all the economic sections of the Summa Theologiæ (and other writings) with a brief summary and a link to the words of the Angelic Doctor himself. An explanation of how to read citations from the Summa can be found here.
I-II Q2. A1. “Whether man’s happiness consists in wealth.”
In this article, Thomas makes the important distinction between ‘natural’ wealth (useful goods) and ‘artificial’ wealth (money, also known as exchange-value) and defines the purpose (telos) of both (co.). He compares the natural, limited desire for natural wealth against the disordered, infinite desire for artificial wealth (ad. 3).
I-II Q105. A2. “Whether the judicial precepts were suitably framed as to the relations of one man with another?”
In this article, Thomas explains the economic justice provided by the Law of the Old Covenant. He explains how the Law commanded ‘regulations in the matter of possessions’, economic equality, and a mixture of private and common property (co.). He praises and defends the social practices of the Law, such as gleaning and hospitality (ad. 1), rejecting the free market (ad. 3), jubilees, debt forgiveness, and the ban on usury (ad. 4), and protections for wage-laborers (ad. 6).
II-II. Q61. “The parts of justice.”
In this question, Thomas describes the two kinds of justice: commutative (justice between individuals) and distributive (justice between the public authority and its citizens). He explains that distributive justice “distributes common goods proportionately” (A1, co.), that “equality is the general form of justice” (A2, ad. 2), and the different forms of debt (A3, co.).
II-II. Q66. “Theft and robbery.”
In this question, Thomas explains that “God has sovereign dominion over all things”, but that human ownership is legitimate, because he created the world to sustain mankind (A1, ad. 1). He lists three reasons for private property and makes note that “man ought to possess external things, not as his own, but as common” to provide for those in need (A2, co.). Thomas states that community of goods comes from natural law, and that the ownership of possessions “is not contrary to the natural law, but an addition thereto devised by human reason [i.e. ius gentium, the law of nations]” (ad. 2). After making distinctions about the mortal sin of theft (A3-A6), he clarifies that “in cases of need, all things are common property, so that there would seem to be no sin in taking another’s property, for need has made it common” (A7, s.c.) and that “it is no robbery if princes exact from their subjects that which is due to them for the safe-guarding of the common good, even if they use violence in so doing” (A8, ad. 3).
II-II. Q77. “Cheating, which is committed in buying and selling”
In this question, Thomas asserts that all commodities must be sold at their “just price” (A1, co.), not based on market price (ad. 1) or marginal utility (ad. 3). After discussing the need for honesty in trade (A2-A3), he discusses the morality of trading for a profit. He distinguishes ‘natural exchange’ of commodities, “which is commendable because it supplies a natural need”, and the exchange “of money for money, or of any commodity for money… for profit” which is “deserving of blame because… it satisfies the greed for gain, which knows no limit and tends to infinity.” Thomas states that commerce can only be conducted without sin if it is for “moderate gain” for the “the upkeep of his household, or for the assistance of the needy” or if he imports useful goods and receives “payment for his labor” (A4, co.).
II-II. Q78. “The sin of usury”
In this question, Thomas explains that “to take usury [interest] for money lent is unjust in itself, because this is to sell what does not exist” and that “just as a man is bound to restore other ill-gotten goods, so is he bound to restore the money which he has taken in usury” (A1, co.). He cites Aristotle to show that usury is contrary to natural law: “the Philosopher, led by natural reason, says that ‘to make money by usury is exceedingly unnatural’” (ad. 3). Thomas clarifies that any form of rent (also called ‘usufruct’) must be done at a just price, equal to the value of the use of the property during the time it was rented (ad. 5), that shareholding co-operatives are legitimate (A2, ad. 5), and that selling on credit and taking interest or fees is a form of usury if the total payment exceeds the just price (ad. 7). He concludes that it is not sinful to suffer the injustice of taking out a usurious loan (A4).
II-II. Q187. A3. “Whether the religious are bound to manual labor?”
In this article, Thomas states the four purposes of manual labor, i.e. work: 1) obtaining food, 2) removing idleness and its temptations, 3) curbing concupiscence and doing penance, and 4) providing alms to others. He states that the necessity of work comes from natural law and clarifies that diverse kinds of work (intellectual, service, and skilled labor) are legitimate and necessary for the common good (ad. 1). On the division of labor, also see SCG III 134:2.
In this chapter, Thomas says that a flourishing society requires a healthy climate, “for civil life presupposes natural life, whose health in turn depends on the wholesomeness of the air” (§ 129). He also emphasizes the importance of an unpolluted watershed: “But of all things put to use as nourishment, water is used most frequently both as drink and food. Nothing therefore, except good air, so much helps to make a district healthy as does pure water” (§ 132).
In this chapter, Thomas argues that economic self-sufficiency is more dignified, safe, and conducive to the preservation of civic life, than reliance on trade (§ 135-138). He warns of the corrupting danger of markets: “Since the foremost tendency of tradesmen is to make money, greed is awakened in the hearts of the citizens through the pursuit of trade” (§ 139). He clarifies that limited trade can be useful for finding “the necessaries of life”, since no one place can produce everything; “Consequently, the perfect city will make a moderate use of merchants” (§ 142).
For further reading, also see Thomas’s Commentary on Aristotle’s Politics. Section I.6-9 (pages 42-66 in the linked ebook) discusses money-making and the evil of the profit motive, while section II.4 (pages 95-100) discusses the error of socialism, i.e. the abolition of private property.