This paper states the single primitive law of the Void Dynamics Model. VDM does not begin from many independent primitive axioms, many independent primitive invariants, or a list of unrelated foundational laws. It begins from one primitive invariant: unresolved twopole opposition borne internally by one admissible origin-condition. Because that invariant cannot discharge into either isolated pole, it must continue articulating itself wherever lawful articulation remains possible. The universal trigger is therefore not arbitrary growth but saturation under non-discharge: when the currently admitted articulation class has exhausted its lawful invariant-bearing capacity while unresolved burden remains, same-domain continuation fails, void debt begins at the saturation limit, and orthogonal re-articulation into a new irreducible domain is forced.