In the sixth century the philosopher–theologian John Philoponus challenged traditional Trinitarian theology, which posited a common substance which is immanent in the three divine persons and binds them together. He declared that each person was a substance of its own and that the common divinity was only a mental construct. Chalcedonian theologians reacted to this provocation by developing a variety of ontological models which sought to preserve the unity of God. In these models an immanent common substance played no role since their creators’ understanding of the order of being was not substantially different from that of Philoponus. Pamphilus insisted on the absolute transcendence of God, which made it impossible to analyse God’s being. Eutychius of Constantinople focused on the genetic link, equating the Father with a species consisting of one item, which then multiplied itself in producing the Son and the Spirit. Leontius of Jerusalem turned the common nature into an Aristotelian first substance and reduced the hypostases to qualities of this substance. Anastasius of Sinai conceived of the common nature as a quasi-hypostasis, attributing to it qualities that had traditionally been reserved for the first hypostasis, the Father, with the result that the common nature became the ‘mother’ of the three hypostases Father, Son, and Spirit. The view of Maximus the Confessor is more complex; by declaring that the divine substance is not a mere mental construct but self-constituted he seems to abandon the Aristotelian framework and replace it with a Platonic one.