Within the conceptual system of scholastic theology, no real question remains once the Trinitarian doctrine itself has been presupposed(i.e. once the linguistic usage of the New Testament has been taken to conform to that of theology): the word and concept ‘God’ signifies (significat) the Person to whom the divine nature is proper; and so ‘God’ can stand for (supponitur)each of the three Persons who possess this nature, or again ‘God’ can stand for all three Persons together. When, for example,the Logos is called ‘Son of God’, ‘God’ in this predication stands for the Father, in so far as he is one of the divine Persons, for ‘God' can stand for each of the three Persons, while the Father alone has a Son. Or again, in the statement, ‘God creates the world’, according to the conceptual system of Latin theology ‘God’ stands for the divine Person, this time indeed for the three Persons together, in so far as they are one God by reason of the unity of nature and thus one Source of the world by reason of the unity of their operation ad extra. For the theology of the Schools, then, ‘God’ is one with respect to the general concept of personality, if we may so put it, and consequently can stand for each of the three Persons individually and for all three together. Once more we do not of course wish to deny that such a view of the concept and the word ‘God’ is possible, legitimate and in the long run unavoidable. But the question nevertheless remains whether this is also the usage of the New Testament.
See Theological Investigations, page 101