That the Existence of God cannot he characterised by the addition of any Substantial Differentia*

IT is impossible for anything actually to be, unless all things exist whereby its substantial being is characterised. An animal cannot actually be without being either a rational or an irrational animal. Hence the Platonists, in positing Ideas, did not posit self-existent Ideas of genera, seeing that genera are characterised and brought to specific being by addition of essential differentias; but they posited self-existent Ideas of species alone, seeing that for the (further) characterising of species (in the individuals belonging to it) there is no need of essential differentias.* If then the existence of God is characterised and receives an essential characteristic by the addition of something else, that existence will not of itself actually be except by having that other thing superadded to it. But the existence of God is His own very substance, as has been shown. It would follow that the substance of God could not actually be except by something supervening upon it; and thence the further conclusion would ensue that the substance of God is not of itself necessarily existent, the contrary of which has been shown above (Chap. XV, n. 4)

2. Everything that needs something superadded to enable it to be, is in potentiality in respect of that addition. Now the divine substance is not in any way in potentiality, as has been shown XVI), but God's own substance is God's own being. Therefore His existence cannot be characterised by any superadded substantial characteristic.

1.23 : That in God there is no Accident
1.25 : That God is not in any Genus