A first aspect of the thirteenth-century discussion is related to the ‘ontological extension’ of matter, that is, Ibn Gabirol’s universal hylomorphism opposed to the corporeal hylomorphism (Aristotle, Avicenna, Averroes). In general, the Franciscan thinkers tended to accept the theory universal hylomorphism, and some of them (Bonavenure, Bacon, Peckam, Olivi) defended this perspective throughout their philosophical production. Others (Duns Scotus, Ockham) did not adhere to this theory, but agreed with the implicit correlate of Ibn Gabirol’s position, the theory of plurality of substantial forms. In further cases (Albert the Great), this doctrinal point was diffusedly discussed, while some thinkers (especially Aquinas) dedicated fiery pages to the refutation of the ‘Gabirolian errors’. The first task of the proposed research will be to clarify the development, mutual interconnections, and shared sources of this debate, pointing out the theoretical reasons which caused the progressive abandonment of universal hylomorphism.

Connected to the problem of the ontological extension of matter is the question on the number of existing matters. While the tradition seemed to be coincident in claiming the existence of one matter only, which is common to every corporeal being (or caused being in general), on the one hand, the radical differences among genera and, on the other hand, the necessary justification of the differences among the matter/s of individual beings (i.e., the principle of identification), made the traditional account more problematic to accept. In some cases — and often from opposite viewpoints — medieval philosophers firmly continued to accept the existence of a single matter (Bonaventure, Aquinas), and consequently they tried to find elsewhere a principle of individuation and material distinction. In other cases, the solution was to suppose a varying number of matters (three different matters progressively informed for Bacon; two matters, corporeal extended and spiritual unextended matter, for Olivi); or even to admit an intrinsic division of matter, always already individuated into particular matters (Ockham).

How are these different solutions connected to the problem on the ‘ontological extension’ of matter? From a universal hylomorphic perspective, are Bacon’s and Olivi’s position admissible? And, finally, what are the conceptual consequences of admitting a plurality of individuated matters regarding the notion of matter? The research herein proposed will deal with these and further questions, underlying the origins of this problem through the analysis of the Arabic sources and their interpretation of Aristotle.

Beside Ockham’s position, the most common solution to the problem of individuation and persistence of matter was to appeal to the quantitative and/or extensive dimensions of the substrate. The admission of a potential and undetermined state of matter implied the necessity of an external cause of individuation/preparedness of matter before its union with the substantial form: if matter is the common substrate of every form, not every form joins the whole of matter, but a single substantial form informs a specific portion/region of matter. By this, the individuation of matter had to be caused by something non-substantial (i.e., an accident) which joins matter before the substantial form.

Since this accident had to perform the individuation of matter, in general, into a particular region of matter prepared to receive its form, the thirteenth-century philosophers often identified this accident with the extension or quantity of matter. On the one hand, echoing Avicenna, Aquinas elaborated his famous doctrine of ‘matter marked by quantity’ (materia quantitate signata), stating that an accidental quantity individuates matter and persists through the substantial change. On the other hand, following Averroes, other thinkers proposed different solutions to this problem, based on Averroes’s doctrine of undetermined dimensions (Henry of Ghent) and focused on the ‘quantity of matter’ (Giles of Rome) or the ‘passive extension’ of matter (Walter Burley). In this way, they claimed that matter possesses an accidental determination expressing its potential quantity/extension before being joined to its substantial form: since this accidental determination always accompanies matter, the result of this approach is that the undetermined substrate, matter, becomes marginally determined.

This tendency will find two of its most radical proponents by the end of the century. On the one hand, Duns Scotus—who famously opposed to Aquinas’s materia signata his theory of ‘thisness’ (haecceitas)—stated that matter has a real existence, an actual being that would make even possible, at least to God, its subsistence without any form. On the other hand, Ockham’s claim that matter is essentially divided into particularised parts allowed him to deny any principle of individuation and corporeity. The debate on matter’s individuation and extension marks a crucial development of the notion of matter in the Middle Ages. The problem that the project will address is whether is detectable, or not, a process of progressive characterisation of matter as extended and quantified shared by the philosophers animating this discussion, and what is the impact the Arabic sources had on this process.