De Rervm Natvra Constantivm Scientia, Principiis Et Affectionibvs Commvnibvs, Dispvtatio

IX. Both seem to have a great connection with truth. However, having entered into the latter, as it is more common at this time, we think first of all: that the acts of the intellect or of the sciences do not produce different species of acts for every diversity of nature that exists in the objects; since it is not even necessary that the acts of the senses be always distinguished by species from the separation of their objects toward which they are directed. Rather, we judge that they must be taken from the difficulty that we perceive in exercising one act or another. Thus, they differ in species either because they create difficulties by reason of the means by which we proceed to understand a conclusion, or because they present singular difficulties—greatly exceeding one another by a wide interval—to the intellect, depending on the variety of abstractions by which they are comprehended, being far removed from one another.

X. That acts are separated from one another in the former way is indeed a probable opinion, but it has a disadvantage attached to it: if it were true, one would have to separate all acts of the intellect that bring different difficulties to the intellect as if they were contained in different genera. Since this is difficult to believe—given that in acts of the same genus, a diversity of difficulties can be excused—we prefer the latter mode: that the diversity of acts be taken from the diverse abstractions, which, as they are various, include not only difficulties of different kinds, but also bring those between which there is the greatest excess and defect.

XI. For this makes it not improbable: according to the variety of difficulties that exceed one another, in the same order, the acts of the intellect that have a more difficult exercise excel in perfection over others that have an exercise that is not so difficult. If we add to this that a great excess of perfection does not fall into things of the same species, especially spiritual ones, it follows that the acts themselves differ from one another in species.

XII. With this posited, the sciences must be one insofar as the abstractions they use are contained in the same species. This results in Physics being a science that is one in the lowest species; since, because the operation it employs in knowing things that are included in its scope abstracts from matter and sensible things by the same reason—namely, only according to individual conditions—it must be contained by an abstraction of one genus.