In differing from Denys, Aquinas recognised how much he owed him. If Rudi te Velde's treatment of the relations between Thomas and Denys be correct, the key to how Thomas will relate participation and substantiality may well have come to him from Denys. [cxxiv]
In Thomas' treatment of the divine intelligence, God is called truth. God is named truth because of an act of comparison or self-reflection. God compares the divine ideas with creatures totally existing by a caused imitation of the divine being as idea.[cxxvii] God is the truth of things so far as their substantial being in its particular grade and character is a participation in divine being, not absolutely, but as thus imitable and imitated.
Underlying is the Iamblichan - Procline notion that, between the unparticipated and the participating, a middle must occur. This becomes, for Denys in this context, the idea that creatures cannot participate the divine being directly, but instead participate its likeness. In Thomas a divine self-reflexive activity is involved to a degree Denys would have found difficult and a pagan Platonist impossible. Thus, Thomas can far more resolutely predicate being of God than Denys or Porphyry can.