Probability and Moral Uncertainty in Late Medieval and Early Modern Times

This dissertation is a study of the concept of probability and solutions of moral uncertainty problem in the late medieval and early modern period. The term probabile was frequently used in medieval and late medieval moral thought. Many scholars have argued that the medieval conception of probability did not have much in common with the later modern and scientific notions of probability. It is a common view that the emergence of the modern notion of probability took place during
the heated dispute about the moral probabilism of the Jesuits in the Roman-Catholic Church in the second part of the 17th century. The probabilismdiscussions included various attempts to present a definition of probability.

Probability was usually defined as the approvability of an opinion by qualified authorities or experts. This interpretation was based on Aristotle’s concept of ëndoxon in the Topics. Contrary to what has been maintained this notion was not merely subjective or epistemic. Thomas Aquinas and Boethius of Dacia thought that in some cases this kind of probability was derived from a consideration of objective risks. Probability was understood as synonymous with the quasi-statistical terms ut in pluribus and ut frequenter, which terms were utilized in connection with the consideration of certain objective risks, e.g. in jurisdiction and business.

One explanation for the emergence of moral uncertainty discussions and probabilism dispute is the Franciscan-voluntarist view of the psychology of moral decision-making. Will exerts a certain dominion over intellect. In a condition of uncertainty will is able to affect the ultimate conlusions of practical intellect, i.e., conscience. In the voluntarist theory of moral action, compliance with law was contrasted with the freedom of an individual more sharply than earlier. This became the general starting point of the 16th and 17th century discussions about probabilism. This is clear especially in the probabilism of Suárez.

The probabilism of Medina and Suárez tends to give the freedom of an individual preference over an individual’s obedience to probable precepts of law. The probabiliorism of Thyrsus González in the 17th century emphasizes the authority of an individual’s conscience. Contrary to Medina and Suárez, González does not accept uncertainty about the existence of a prescription of law as a justification for acting free as if that prescription would not exist.