Trained in Alcalá, Spain, and Paris, France, before being made professor of Philosophy at Alcalá in 1520, he left academia in 1524 to join the Dominicans and returned to take the chair of theology at Salamanca University in 1532. He is best known in economic theory and theological circles for his writings defending the price differential in usury as compatible with "just price" from the perspective of the Thomists. He held powerful positions, including Confessor of Holy Roman Emperor Charles V and the emperor's representative at the Council of Trent.
Thought
Usury
De Soto was concerned about the complexity that had emerged from unclear moral standards of usury. He complained that the merchants had invented convoluted schemes in order to meet the conflicting demands of church leaders. His position should be seen within the background of his Franciscan background and historical context. De Soto was involved in an active debate in the medieval era on the sterility of money and the requirements of natural law given this sterility. His rationale on interest is explained by Langholm. Woods and D'Emic characterize de Soto's attitude toward usury in significantly different ways. D'Emic reports that De Soto thought voluntary contributions given from borrower to lender in gratitude were acceptable, but strictly forbid the lender from pressuring the borrower. He also asserts that De Soto thought permitted lenders to hope for such contributions along with other motives of benevolence and friendship, but regarded the sole motivation of financial gain as immoral "mental usury". Woods, on the other hand, reports that De Soto did not believe Christ had declared usury to be sinful at all, and did not believe that had anything to do with lending at interest.
Law
In 1556, Soto published a treatise on law, De Justitia and Jure, that is considered a foundational text in the general theory of international law. Like his teacher Francisco de Vitoria, Soto condemned the Spanish conquests in the New World.
Mechanics
Domingo de Soto was the first who stated that a body in fall experiments a uniform or constant acceleration, this being a key concept in physics, which was essential for the posterior studies of the gravity laws by Galileo and Newton. In the 20th century, Pierre Duhem credited him with important achievements in dynamics and viewed his work as a forerunner of modern mechanics.
Works
Summulae, 1529.
De ratione tegendi et detegendi secretum, 1541
, 1544
In VIII libros physicorum, 1545
Deliberacion en la causa de los pobres, 1545
De natura et gratia libri III, 1547
Comment. in Ep. ad Romanos, 1550
In IV sent. libros comment. 1555-6.
De justitia et jure libri X, 1556
Jaime Brufau Prats and Sixto Sanchez-Lauro, eds. Domingo de Soto, OP., Relecciones y opúsculos.
