Commercium Without Common Ground: Why Interaction Does Not Require a Common Origin

In Section IV of the Inaugural Dissertation (1770), on the principle of the form of the intelligible world, Kant argues that substances can be in commercium, and so belong to one world, only if all of them depend on one being. I state the inference as a Common-Ground Principle (CGP), relativized to the world in which the interaction obtains, and refute it with two finite countermodels: members of lineages with distinct first grounds jointly produce an event and stand in a real relation, yet no unified origin generates both. The countermodels rest on three claims: interaction does not imply constitutive dependence; pure relations cannot bridge distinct origins; distinct first grounds need not be related. All three are Kant's own commitments. The one premise the Kantian countermodel violates identifies the principle of the world's form with the principle of its substances' existence, and a parallel conflation underlies Kant's claim that necessary beings cannot interact. What makes commerce possible is a shared form: the items' being typed within one ontological space. The unity of such a space is not the unity of an origin and requires no common origin of what the space contains, as original spaces, which have no ancestry, show. Where no space is shared there is no commerce, only convergence: the genesis of a new unit in which continuants of both lineages are typed.