CHAPTER XXIV—That the Existence of God cannot he characterised by the addition of any Substantial Differentia⁵¹⁵¹This and the next chapter go to show that the logical arrangement is inapplicable to God, by which genus and differentia together constitute the species or definition, as animal and rational make up man.

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.⁵²⁵²There is an ideal or typical man in the Platonic scale, but no ideal animal. The former is specific in reference to Socrates, the latter would be generic. The type stops at the species. This piece of Platonism is not formulated in the writings of Plato. 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 (Chap. XVI), but God’s own substance is God’s own being. Therefore His existence cannot be characterised by any superadded substantial characteristic.