A. On the First Way of Instantiating, that is by Efficient Causality

138. In the first way I say that a created supposit cannot instantiate a nature other than its own, because the other nature is only in obediential potency to such a union with Christ, for otherwise it would exist by violence in its own supposit (as a heavy thing going upwards); obediential potency in creatures has regard to the efficiency of the first efficient cause and not to any other active power.