“Combining a full command of earlier scholastic authorities with a hitherto unprecedented grasp of market phenomena, Lessius provided fresh insights that challenged traditional economic doctrine in authoritative fashion. He is, certainly, the foremost continuator of the Spanish school of economic thought. Further, he has claims for consideration as a major contributor to the development of economic analysis.” (Gordon, Economic Analysis before Smith).

“His work On Right and Justice is conceived as a commentary on the Secunda Secundae of Thomas Aquinas’ Summa, with one book devoted to each of the cardinal virtues; however Book II (Justice), which goes far beyond Aquinas’ text, occupies four-fifths of the entire work. It is a notable contribution to jurisprudential literature. First published in 1605, it was reprinted the following year in Lyon and in Paris, in 1617 in Venice and during the author’s lifetime alone twenty editions were issued, several of which included the appendix on the montes pietatis. Book II, ch. 20 deals with usury, and ch. 21 and 22 with exchanges and annuities. His economic teaching was in the tradition of the Spanish moralists, such as Azpilcueta and Covarrubias. He minimized the importance of the Bull Cum Onus promulgated by Pius V in 1568 against the rent-charges. He also defended the triple contract and held that the montes were justified in charging interest to reimburse administrative expenses.
He knew Antwerp business well, including the Antwerp Exchange of which he wrote: “…the practice of the Bourse of Antwerp, where the merchants gather every day and take account of the abundance or shortage of money, of the number of exchanges, of the amount of merchandise and all other sources of gain in which there is need of present money. Then either by themselves or their agents they establish the price for the privation of money. Merchants who lend may demand this price for the reason that they are deprived of their money for such and such a time and may not call it back before the time agreed. This price is sometimes 6% per year and sometimes 7%, 8%, 9%, 10%, 11%, or 12%; more than twelve percent they are forbidden to demand by the Constitutions of Charles V…” (Houkes, pp. 369-70)

For centuries Lessius’ work was to some extent forgotten. Joseph Schumpeter afforded Lessius more than ample mention in his monumental “History of Economic Analysis” which brought him back from obscurity.