Aquinas was concerned with the liberty of autonomous persons to conduct their affairs through civil conversation and rational persuasion. He valued highly the practical order of civil society through which each individual gains mastery of his own liberty through the cultivation of habits and virtues. Although it is not likely that Aquinas had formed the idea of natural rights, he did recognize that all men are equal in liberty even though there are wide inequalities and differences with respect to their talents, capacities, and callings. Aquinas spoke of indelible laws in man's being that command the respect of everyone. Society involves the mutual exchange of ideas, products, and services for the sake of a good life to which its many individual members contribute.

          Aquinas explained that government agents had certain limits beyond which they could not function. They are bound by laws of human nature that emanate from the act of God's creation. It follows that positive laws that are inconsistent with man's nature should not be enacted or should be overturned. Positive laws must be just and must be derived from general principles of natural law. An ordered society under human laws applies to people at their natural level. Therefore, to ensure an ordered society, human laws must be constructed.

          According to Aquinas, a ruler is needed even in the state of perfection or innocence in order to provide direction and guidance. He adds that, although people require an orderly political life, the authority of government agents ought to be limited. Tyranny is illegitimate and justice demands that a tyrant be deposed. Aquinas explains that public action, rather than individual violence, is the proper remedy against tyranny. Justifiable resistance is a public act of the whole people. He observes that political authority exists originally in the whole people organized as a civic community. It follows that there is no power to frame laws except as representing the people and that legitimate title to power is the result of a transfer by the rational act and consent of the community.

          Aquinas held the idea of the limited scope of government authority. Although he posited no real theory of the hypothetical best regime for the ideal community, he favored a mixed regime for the real world. He says that the regime worthiest of the human person mixes the best elements of monarchy, aristocracy, and democracy. This mixed regime would be limited by moral law and legal or constitutional devices to prevent arbitrary use of power. Realistic and pragmatic in his thinking, he saw that a mixed government would be the best practical type, would require consent and permit moral freedom, would minimize the danger of tyranny, and would allow people to believe that they had a say and a stake in the community.

          For Aquinas, the political community is the sovereign construction of reason. He says that the political sovereign has authority to legislate from God and is therefore responsible to God. Accordingly, law should advance the common good. In his writings, Aquinas linked ethics to politics and the individual human person to the common good. He also emphasized that civilized political institutions respect the human capacity for reflection and choice which provide the foundation of law.

          Aquinas, in the Aristotelian tradition, emphasizes the inexact character of ethics and the mutability of law due to the contingency of specific circumstances. He explains that law can be adapted to time and place and properly changed due to changed conditions of men. What is just depends upon the circumstances. He adds that legislators must also consider and test the usefulness of possible rules to determine that which is most appropriate to be law. Aquinas maintains that utility is an important standard or criterion for ascertaining the justice of legal rules. Usefulness is a standard for discerning when a law should be changed. Law is not to be imposed once for all time. Observing that moral and legal reasoning is an inexact science, Aquinas states that good law is created through past experience and the consideration of pertinent social circumstances.

          According to Aquinas, the function of positive law is mainly to embody and give coercive force to the principles of natural law in the form of authoritative direction. Recognizing the limits of law in the production of virtuous citizens, Aquinas teaches that law should not directly dictate the exercise of all the virtues nor directly forbid the exercise of every vice. True virtue consists in using one's reason and free will in making the right choices. For Aquinas, the primary practical problem of an individual's moral life is to decide what to do in the unique circumstances in which each unique person finds himself.

          He stressed that political authorities should be concerned with broad matters of general interest rather than with small details of individual conduct. No laws are capable of anticipating every particular circumstance to which a law be applied. It follows that laws should be stated in general terms, expressing what is proper for cases of most frequent occurrence. There may be situations in which a law that is applicable to most cases would produce an injustice if rigidly applied. Aquinas, therefore, suggests permitting the judge to have the power of equity that allows him to moderate promulgated law in order to achieve a just outcome.

          Aquinas understood that custom can create, abolish, or amend law. He favored law that was consistent with prevailing customary practices. Custom is an expression of widespread human rationality and not just the product of the articulated rationality of a select few. Aquinas was committed to liberty, loved tradition, and had a sense of realistic hope and moderate institutional progress.

          Aquinas addressed a number of economic questions particularly in Summa Theologica II, II. Among the topics covered are the division of labor, property rights, the just price, value theory, insider trading, and usury, among others. Although he said there was something ignoble about trade, he also recognized the usefulness of merchants whose activities were to the community's advantage. Aquinas taught that the operational principles of the economic order are subordinate to the moral and political ends of the city. His justification of mercantile profits offered many examples of the benefits that commerce could bring to society.

          Foreseeing Adam Smith's division of labor theory, Aquinas explained that diversification of men for diverse tasks is the work of divine providence and stems from natural law with different men possessing abilities and inclinations for different occupations and functions. He recognized the benefits of exchange and the division of labor in satisfying the needs and wants of individuals.

          Aquinas views private property as necessary for human life and as an extension of natural law. He acknowledges that under natural law all property is communal, but also contended that the addition of private property was an extension, and not a contradiction, of natural law. Aquinas explains that human reason derives the notion of distinction of possession for the benefit of individual human lives. He states that possession of private property is necessary because: (1) men will more resolutely and attentively take care of things if they possess them instead of the goods being held in common by all or many others; (2) possession advances order rather than chaos and confusion as responsibility can be determined; and (3) private possession promotes a more peaceful state. Aquinas realized that, not only does creativity require property, without property under the dominion of every person the individual's liberty of action is diminished. He accepted an unequal distribution of private property but also approved of the regulation of private property by the state. He also said that while the ownership of goods should be private, the use of goods must be in common (so that the poor and needy can have their share) or must be in service of the common good.

          It is difficult to judge precisely what Aquinas meant by the term "just price." The various interpretations of what he meant by just price include, but are not limited to: (1) an equivalence in terms of labor cost; (2) an equivalence in terms of utility; (3) an equivalence in terms of total cost of product; and (4) market price.

          When speaking of the "just price" in an organized exchange, Aquinas often appears to mean the price that is paid in a more or less competitive market. Noting that exchange takes place for the utility of both parties, Aquinas states that the norm of commutative justice is expressed in the principle of equivalence between reciprocal contributions. Accordingly, there needs to be a certain equivalence or proportion between what is given and what is received. Aquinas describes commutative justice as the principle of absolute equality in exchanges of goods and services among individuals. He explicitly repudiated the notion that prices should be determined by one's position or station in life, noting that the selling price of any commodity should be the same whether or not the buyer or seller is poor or wealthy.

          For Aquinas, the valuation of goods does not seem to depend upon any intrinsic property of the goods themselves. The equality to which Aquinas frequently refers appears to be the mutual satisfaction gained by each contracting party in an exchange. Aquinas also observes that the one element that measures all products and services is the need that involves all exchangeable goods because all things can be related to human needs. It is apparent that Aquinas was certainly not reducing the value of a good to labor by itself. Recognizing that market forces affect the value that is placed on goods and services, Aquinas is clearly not subscribing to the labor theory of value.

          Aquinas wrote that buying and selling seem to have been introduced for the mutual advantages of the involved parties because one needs something that is possessed by the other and vice versa. He states that when market exchanges occur to meet the needs of the trading partners then there is no question of unethical behavior. However, if one produces for the market in expectation of gain then he is acting rationally only if his prices are just and his motives are charitable. The prices are just if both the buyer and seller benefit and the motives are charitable if the profits are to be used for self-support, charitable purposes, or to contribute to public well-being.

          Aquinas presented a mixed but somewhat benevolent view of trade. He said that while trade may present opportunities for sin, it is not sinful by its nature. Aquinas denounced covetness, love of profit, and avarice but said that mercantile gain was justified when directed toward the good of others.

          The just price for Aquinas is the one, which at a given time, can be received from the buyer, assuming common knowledge and the absence of fraud and coercion. Aquinas anticipates the problem of "insider trading" when he observes that a person may sell a scarce product at the prevailing market price although he knows that more of the product is on the way and will be available shortly. The implication is that there is no moral duty to inform a potential customer that the price of the product that one is attempting to sell is probably going to be lower in the near future.

          It appears that Aquinas, at least implicitly, anticipated the concept of opportunity cost. He explains the idea of price as just compensation to the seller for the utility lost when he becomes detached from the item sold. Aquinas also mentions the benefits supplied by men of commerce when they conserve and store goods, import goods that are necessary for the republic, and transport goods from geographical areas where they are in great supply to places where they are scarce.

          Aquinas, like the Bible and Aristotle, wrongly condemned the practice of charging interest for the lending of money. All fail to see that borrowers are not injured when they take out a loan and, in fact, are likely to benefit if they can invest in a project that yields a return greater than the interest paid. Aquinas says that usury, the charging of money on loans, is sinful and unnatural because money is barren and was simply invented for the purpose of exchange.