“Ubi Natura Facit Circulos in Essendo, Nos Facimus in Cognoscendo.” the Demonstrative Regressus and the Beginning of Modern Science in Catholic Scholastics

chapter ten

“UBI NATURA FACIT CIRCULOS IN ESSENDO, NOS FACIMUS IN COGNOSCENDO.” THE DEMONSTRATIVE REGRESSUS AND THE BEGINNING OF MODERN SCIENCE IN CATHOLIC SCHOLASTICS

10.1 Scholastic and Cartesian Logic

There can be no doubt that the regressus in proof-theory was one of the most important achievements of Venetian Aristotelianism. The classic definition was given by Jacopo Zabarella: Regressus vero est inter causam, et effectum, quando reciprocantur, et effec- tus est nobis notior, quam causa, quum enim semper a notioribus nobis progrediendum sit, prius ex effectu noto causam ignotam demonstramus, deinde causa cognita ab ea ad effectum demonstrandum regredimur, ut sciamus propterquid est.1 The regressus is particularly important when historians of philosophy and science seek to emphasize the progressive significance of the Aristotelian logic of the Renaissance, which is closer to our own period. It is thus surprising that there is no clear presentation of the regressus proof in the rel- evant handbooks of the twentieth century.2 Obviously, this is connected both to logic and to the philosophy of science. But it is surprising3 only when one underestimates the significance for the philosophy of science and the intention of Aristotle’s Analytics, especially the Posterior Analyt- ics, and when one overlooks the double function of that logic, namely, as utens and as docens, since it both sets out how thinking functions in keeping with its own nature, and teaches how thinking ought to function. Presumably under the influence of Descartes (whose Regulae see the understanding as in need of guidance), but certainly on the model of the

1 Zabarella, Liber de regress, 324. Cf. Mikkeli, An Aristotelian Response, 92–101. 2 The best presentation is Jardine, “Epistemology of the sciences;” he describes his presentation as “tentative.” See also Prins, “Zabarella,” and Ganthaler, “Weiterbildung.” Regres- sus is not mentioned in the discussion of Zabarella in Kneale, The Development of Logic, 306f. 3 R. Pozzo seems to be surprised by this: see his article “Regressus/progressus.” 184 chapter ten

Port-Royal Logic,4 which translates the Regulae into the genre of a hand- book, the philosophy of science—the art of thinking (L’art de penser)— was clearly regarded above all as an artificial thinking. Knowledge became the business of emending thinking that was naturally defective. Paradoxi- cally, this was done on the basis of a naïve ontology of ideas that regarded everything as real that is thought clearly and lucidly.5 Accordingly, the syllogisms become less important, since it is not they that generate knowledge, but rather the clear and distinct ideas and the scientific methodology in the sense of regulated induction and teaching praxis. If one looks at the scholastic treatises of the sixteenth and seventeenth centuries, it is at once obvious, as the present study will endeavor to show that the significance of the theory of demonstratio in the Renaissance Aris- totelians lies precisely in the link between the philosophy of science and logic. I shall show, by means of a number of examples that I have selected almost exclusively according to the criterion of easy accessibility, that the school philosophers were concerned with the substantiality of logical argumentations and with the formal comprehensibility of that which is known with certainty. The adaptation, with varying degrees of intensity, of the Renaissance-Aristotelian theory sets out some of its implications, which are of fundamental interest for logic. As we would expect from the way in which the scholastics were aware of the problem, they struggle to save their doctrine from the Scylla of being irrelevant to academic research, but without succumbing to Charybdis of the methodology of the Cartesian enlightenment. From a scholastic per- spective, the ontological status of that which has been gained epistemo- logically is the decisive problem of philosophy. Early modern scholastics are interested not only in clear ideas, but also in objectively true ideas. Naturally, every manual of philosophy contains a section on demonstratio, unless it is already influenced by the Port-Royal Logic. By way of expla- nation, let me recall that the manuals of Catholic scholasticism from the end of the sixteenth century onwards are constructed in accordance with a strongly topical principle, so that it is easy to find out in a schematic manner what they have to say about any particular theme. Calculability (that is to say, the stability of the horizon of expectation) was the precise goal of this genre of manuals. The proof-theory is found towards the end

4 Arnauld and Nicole, La logique. 5 See the chapter on the Pophyrian Tree in this book and the chapter on Suárez in Blum, Philosophy of Religion in the Renaissance.