Abstract

In this paper, I examine a neglected debate between Francisco Suárez and Pedro Hurtado de Mendoza about the unity of composite substances. There was a consensus among the Jesuits on the fact that the per se unity of composite substances requires something in addition to matter and form. Like most Jesuits, Suárez and Hurtado further agree on the fact that this additional ingredient is not a full-blown thing, but a “mode of union.” However, while Suárez claims that the union is achieved through a single mode, Hurtado maintains that it is necessary to postulate two distinct modes of union, one modifying form and another modifying matter. I argue that this disagreement actually reflects an important ontological debate about the nature of the items that serve as the cement of things and that it eventually leads later Jesuits like Rodrigo de Arriaga to conceive of union as a polyadic or “straddling” mode.