Abstract
With this work, Rudolf Schuessler offers the most significant and comprehensive philosophical/historical study of the probabilist tradition extant. A professor of philosophy at the University of Bayreuth, Germany, specializing in matters of moral argument, S. provides for all readers, from the neophyte to the expert, an extraordinarily robust account of the debate, in three parts. The first and most important part includes four chapters that situate the debate both historically and philosophically. Chapter 1 securely nests probabilism and the issue of a plausible or reputable opinion in medieval scholasticism. That is, after introducing the early Aristotelian notion of a plausible opinion as sufficiently acceptable for moral argument, S. engages Thomas Aquinas and other scholastics who similarly appreciated that moral argument was based on reasonable estimation and not on indubitable claims. Through scholasticism, the reputable or plausible opinion emerges as something that others can follow and trust, and warrants not only respect but privilege within moral debate discourse.
Throughout the book, S. demonstrates his command of the debate and in this chapter he brilliantly demarcates “medieval tutiorism” (as used from the twelfth to the sixteenth century) as a commonsensical “safety first rule” that insisted that moral questions be at least adequately considered, from the near-absolute rigorist “tutiorism” that was effectively an anti-probabilist position, and only first recognized as such by Francisco Suarez in the seventeenth century. The distinction is important; seventeenth-century tutiorism spawns not from probabilist sources but from the conservative intolerance often associated with the anti-probabilists.
After a second chapter that highlights the Dominican contributions to moral discourse, S. highlights the emergence of probabilism as a school of thought in 1577. The third chapter, in five sections, is a tour de force, and will inform all subsequent discussions on dating the rise, challenges, and influence of probabilism. Marking the rise of probabilism from 1577–1620, S. then describes it as dominating the mainstream from 1620–1656, while noting that the first “laxist” critiques of probabilism emerge in 1640. The third section, covering the period from 1656 to 1700, marks probabilism under fire. S. interestingly classifies the probabiliorists who emerge in 1656 as anti-probabilists. While I had learned “probabiliorism” as a conservative Dominican development of probabilism—that is, that when adopting a more lenient position one should have weightier arguments—S. defines it in these terms: “it is only permissible to follow the most probable or the safest position from a set of incompatible probable prepositions” (314). S. argues that probabiliorists and the absolute tutiorists, who mandated “the safest side in all cases” (314), were fundamentally opposed to the claims of probabilism that effectively recognized the legitimacy of reasonable opinions by competent authorities. I now realize that S. is right and that the difference between probabilism and probabiliorists was not one of degree or development but rather was outright oppositional. He concludes the third section with a fascinating account of the Jesuit General Tirso Gonzalez, a probabiliorist, who led a significant but eventually failed charge against probabilism that culminated in a so-called “civil war” among the Jesuits between 1670 and 1700. The remaining two sections take us through the eighteenth century and then to the present.
The fourth chapter reflects on the arc of the endoxon, being replaced by the dual concept of probability that measures the intrinsic rational merit of the argument and the extrinsic competency status of the authoritative proponent. In the work’s remaining two parts, S. investigates a variety of topics—first those that emerged before the critical oppositional debate and then those subsequent to it. The second part mostly concerns how the school of probabilism works. The fifth chapter looks at how arguments emerged, selecting them either according to extrinsic (authors) or intrinsic (opinions) probability, while the sixth investigates the differing effectiveness of stand-alone, multiple and majority opinions, and the seventh considers whether ancient or more modern opinions should be preferred.
The third part treats in the eighth chapter the assumptions of the two sides of the debate regarding probability; the ninth, the degrees of probability; and the playful tenth, “a new doxastic voluntarism,” that is, believing what we want. I found the eleventh chapter the most illuminating. How did the penitent as probabilist get treated in the confessional: was it liberty or tutelage that marked the confessor’s offerings to the clever penitent who knew more than a few of the arguments? S. concludes this memorable work on the mathematical calculus of probability.