Probabilism was a major intellectual development within early modern Catholic moral theology, but it is still poorly understood, and misconstrued as a highway to moral ‘laxity’. This is largely due to the thorough satirical trashing by Blaise Pascal and to its association with the equally maligned Jesuits, despite the fact that the latter were neither its sole practitioners nor its original inventors. Over the past decades, however, there has been a renewed interest in probabilism, from both historians and moral philosophers who have started to appreciate it on its own terms as a symptom and tool of intellectual modernization in a period characterised by rapidly expanding horizons of knowledge and a deep shake-up of religious and epistemic certainties more generally. Although William Bouwsma already hinted at this connection vaguely in his Waning of the Renaissance (2000), the most sustained contributions on the problem have been published by Italian, French, and German scholars. Those familiar with the respective polyglot historiography will therefore recognize some of the themes and problems the author tackles in her monograph. Even so, they will appreciate the systematic overview and nuanced analysis Tutino provides. Novices on the other hand will be grateful for the clarity of her explanations that allow following the development and application of probabilism, as well as for her capacity to bring to life what is often dismissed as a sterile glass-bead game of theologians with too much time on their hands.

As Tutino demonstrates with great emphasis, and sometimes with a little too much rhetorical flourish, probabilism was an exciting and productive way of engaging with complex moral problems and a serious attempt to deliver answers in areas of epistemic uncertainty. The development of probabilism was of course deeply connected to the confessional age and the concern with getting people to account for their acts in confession as well as with the confessors’ concern to judge these adequately. Probabilism, which moved moral discussion away from safety and certainty that seemed so difficult to obtain, therefore emerged amongst theologians pre-occupied with sacramental confession like the Augustinian Martín Azpilcueta (aka doctor Navarrus). The Dominican Bartolomé de Medina in 1579 provided the now classic definition establishing a strong distinction between an opinion and doubt, which allowed for a probable opinion, defined as an opinion ‘supported by solid arguments and the authority of learned men’ without obliging the individual to opt for the safest or most probable opinion. As with all definitions, what followed were new queries regarding the exact meaning of the terms—certainty, probability, doubt, opinion. The probabilist debates, as Tutino convincingly argues, were not merely down to the inner dynamics of intellectual controversy and the necessity to clarify the terms and definitions of ‘probability’. There was a real need to engage with the moral conundrums that followed from the challenges to established certainties, ancient authorities, and the very concept of ‘truth’. In an age of expanding capitalism and world-wide trade, probabilism allowed for the modification and adaptation of concepts of usury; in an age of mission, it allowed more flexibility in dealing with the status of the pre-existing marriages of Asian converts. Closer to home, and still casting a long shadow today, was the new position on the timing of the animation of the foetus, when microscopic discoveries suggested that life probably began immediately with conception, contradicting the authoritative Aristotelian calculation of roughly three months.

One of the strengths of Tutino’s work is that her analysis is not only based on the printed outputs of the proponents and critics of probabilism, but that she also examines unpublished manuscripts, including the unpublished appreciations of the censoring bodies (Congregation of the Index and Holy Office). This allows her to flesh out the multiple currents, and the extensive Latin quotations in the endnotes reflect how closely her account follows the documents. As she tracks these developments, she widens the focus beyond the Jesuits who tend to dominate the historical perception.

She, moreover, delivers a compelling history of the shifting meaning and heuristic place of probabilism over time, especially after 1650, when a so-called ‘rigorist’ push-back began. Some of this was due to anxieties over the capacity of probabilism to challenge theological authority by separating it from epistemological authority, but the shift in the international distribution of power, in particular the decline of Spanish hegemony and its repercussions on the Curia, as well as the knock-on effects on church–state relations more widely, also mattered here and became often enmeshed. Eventually, this led to a cautious containment strategy, by which ‘excessive’ individual probabilist statements were condemned but probabilism as such was not banned. Tutino makes an important intervention by arguing that probabilism was neither per se laxist nor authoritarian; it could be both. It could trigger innovation and help to navigate competing authorities by allowing to follow probable opinions where certainty was an impossible thing to achieve. Simultaneously, and for the same reason, it could support theological authority and ecclesiastical hierarchy by providing a hermeneutic tool to manage and contain the centrifugal forces emanating from the multiplication of opinions and the dwindling sphere of certainty. Often maintaining a productive doctrinal ambiguity, probabilism was useful to keep a broad church on the road without too many wheels coming off.

Tutino does not hide that she intends to make a highly personal intervention, and sometimes the incessant use of the first person singular or plural, which makes the reader permanently part and sometimes party of the discussion, can feel manipulative. Another choice—probably not down to the author but the publisher—is more problematic and in my view detrimental to the book’s utility for the scholarly reader it addresses: it does not contain a bibliography by which one might easily trace the manuscripts, printed sources, and the historiography that have informed her study. One can piece this together by picking through the 180 pages of endnotes. Given the character of the book (and its length), this is not only very user-unfriendly, it also undermines the ambition to render the history of probabilism as well as the state of the debate on it more transparent.