Mind the Economy/Justice 119

From Aristotle to algorithmic markets, when is a price the right price?

28 September 2025

7' min read

There is a thread that runs through the economic and moral history of the West like a karst river that flows underground and from time to time resurfaces: it is the idea that the price of a good is not just a 'price', but represents a moral, political and cultural judgement on what is fair and just. Charles R. Geisst reconstructs the fascinating history of this idea leading us from Aristotle to Roman jurists, from scholastic theology to the transformation of the 'just price' into the law of one price in modern markets (Just Price in the Markets: A History, Yale University Press, 2023).

Aristotle: price as ethical judgement

Aristotle does not write an economics textbook; his reflection on economic matters is essentially ethical and political. And even the question of price appears in the Nicomachean Ethics and Politics as a problem of justice: exchange is not just the exchange of goods, but social relations. Far from being a purely utilitarian measure, the 'just' price for Aristotle achieves a proportion, a correspondence that maintains the balance between the parties and preserves reciprocity within the pólis, the community. Two points are essential. The first concerns the distinction between 'distributive justice', which must preside over the allocation of honours and resources according to merit or necessity, and 'commutative justice', which instead concerns the cost of exchanges and the distribution of the benefits derived from them. Reflection on just price moves within the realm of commutative justice. It is not an abstract number, but the result of a judgement that holds together the buyer's need, the social function of the good and the producer's contribution. The second point concerns the concept of chreía, of need. For the Athenian, value arises from the ability of the thing to meet human needs. Currency, then, is a conventional invention to make the effectiveness of such responses comparable. This perspective explains, among other things, the harshness of the condemnation of usury. Money that 'generates money' without passing through labour or social use is a deviation from the teleology of economics towards what he calls chrematistiké, pure accumulation for its own sake. To say that interest is 'sterile' was for Aristotle not a petty technical observation, but an ethical diagnosis: a system that treats money as an autonomous source of value disintegrates the harmony of civilised life. There is no 'formula' for the right price. The basic idea in the Aristotelian framework is that price is judged in the context of the polis. It is a statement that, read today, reminds us why even markets always need social norms, trust, clarity, and a shared idea of fairness in order to be efficient.

It was the Romans who transformed ethical intuition into concrete legal instruments. In Roman law, the contract of sale requires a certain price and an agreed will. However, Roman jurisprudence does not ignore the moral question either: the institute of laesio enormis (enormous injury), which provides for the possibility of annulling a contract of sale if the good is sold at a price less than half its value, reflects the concern that a formally valid exchange may, however, be substantially unjust.

This marriage of written rule and moral principle constitutes an early bridge between Greek philosophy and the commercial practice of the following centuries.

The friar who challenged the merchants

In the medieval Christian world, the Aristotelian heritage is taken up and developed first and foremost by Thomas Aquinas, who continues to consider the fair price as a moral criterion that avoids harm to others and promotes the common good. In the 15th century, philosophical and ethical reflection on the market and finance took a leap forward, thanks above all to Bernardine of Siena. Not only a tireless preacher, but also one of the first to rigorously question the moral rules of economics. In his De Contractibus et Usuris of 1471, Bernardino tackles head-on the thorniest topics of commercial practice at the time: contracts, sales, loans and usury. And he does so with a simple but revolutionary principle: the right price is the one that protects both parties and respects the balance of the community. Bernardino's judgement is also clear against the practice of selling off the market, which involved charging an abnormal price when buyers were foreigners. His position on the legitimacy of imposing an interest is extremely modern. Bernardino, in fact, recognises a value to time. Selling wheat today at one price and delivering it tomorrow at another may be right, provided the variation results from natural circumstances and not from pure speculation. Bernardino thus appears as a forerunner of a market ethic: he does not deny the logic of trade, but seeks to regulate it, preventing the quest for profit from degenerating into injustice. With Bernardino, the market place becomes a moral laboratory, where the contract is not just a bargain, but an act of mutual responsibility. The community is always the reference level of judgement. Those business practices that undermine trust are to be considered unjust even if formally legitimate.

From the square to the single price

From the Renaissance onwards, the conception of price undergoes a profound transformation. Mathematics, accounting, the expansion of international trade and the standardisation of currency shift the axis of discourse and the 'right price' becomes identified with the 'single price'. Thus the so-called 'law of one price' is born. When markets are perfectly competitive and transaction costs are low enough, the same good must have the same price everywhere. If an apple costs 1 euro in Milan and the same apple costs 0.80 euro in Rome, traders can buy apples in Rome and sell them in Milan, earning on the difference. This arbitrage process will tend to align prices until the apple is sold at the same price everywhere. Pacioli's double-entry game, the development of financial tables and banking practices, and the reflection on money and debt that accompanied the emergence of nation-states are all crucial stages that contributed to the identification of the 'right price' with the market price and morality with efficiency. But as Geisst reminds us, the question of the right price does not disappear because even efficient markets can generate ethical problems: inequality, speculation and systemic crises.

The Right Price in the Age of Finance

In the 20th century, complex finance shifted the focus to risk, its measurement and pricing. While highly sophisticated mathematical models and the expansion of electronic trading made real-time pricing possible, algorithmic finance and ever-increasing global leverage multiplied potential gains but also systemic risks. The Aristotelian ideal of a price that preserves the community seems to be dissolving in the search for ever higher returns, but the question of 'just' does not disappear. It resurfaces forcefully in times of crisis but still too little in political debates on regulation and redistribution despite the fact that geopolitical events call for deep and shared ethical reflection.

Energy, vaccines and minimum wage

The energy crisis of 2021-2022, for example, after the pandemic and with the war in Ukraine has shown the fragility of market mechanisms and the need for decisive economic policy interventions to avoid terrible social shocks. So when can a price be considered fair in such cases? Or think of COVID-19 vaccines. Bilateral contracts between states and manufacturers have generated differential prices and discriminatory access to treatment. What is the fair price when global public health is at stake? A final example is the minimum wage and the price of labour. Leave it to the play of supply and demand or the bargaining power of trade unions and employers' organisations to determine, or establish by law that labour is not a commodity like any other, it is an instrument of emancipation and contribution to the common good and therefore cannot be priced like other commodities. The political debate on the appropriateness of introducing legislation for the identification of a 'just' wage mixes arguments that have to do with different conceptions of fairness, concern for social stability and the protection of economic competitiveness.

The age-old reflection on the question of the right price therefore appears to be highly modern. The fair price question, in fact, returns whenever the market touches fundamental goods such as health, the environment, labour, social cohesion and when price dynamics exert strong distributional impacts.

The historical evolution of the debate suggests that the idea of 'fair price' has never been and can never be a stable mathematical rule. Instead, it is a regulatory idea that changes shape with the times and with changing techniques and practices. It is an idea that transforms but does not disappear: from an Aristotelian ethical principle, to a Roman legal instrument, through medieval moral sensitivity, to the modern economic law of 'one price'. And today, in the time of algorithmic finance and globalised politics, where prices can become weapons, the 'right price' has become primarily an issue of governance. It is no longer just a question of how much a good is worth on the market, but whether and how that price reflects shared principles of fairness. From the energy bill to vaccines, from the minimum wage to the digital tax, prices are now levers of political power and instruments of redistribution, capable of redrawing social and geopolitical balances.

The debate on fair pricing, then, brings out two fundamental needs: the rooting of economics in ethics and the need for strong global institutions capable of coordinating, regulating and, if necessary, limiting market mechanisms. Without this rootedness, prices risk becoming a pure reflection of power relations, losing their function as a shared measure of human value and need. The devastating effects of reducing the economy to technology and renouncing political multilateralism are there for all to see. This perhaps means that the real question can no longer be "how much?" but "at what price?".