A. What is to be Understood by ‘Personal Union’

14. About the first I say that union does not state anything absolute in a supposit, because when anything absolute is understood in one of the extremes no perfect idea of union is understood, because union is not understood in relation to itself. Therefore whether union is concomitant to something in one extreme or in both, since it is not nothing, it does at least state a respect; but not a common respect, which would be of the same reason in each extreme (of the sort that likeness is), because the disposition in the assumed nature and the assuming person is not of the same reason. Now the assuming person has no real relation to the created assumed nature, from Book I distinction 30 nn.49-51; conversely, however, unless the assumed nature had some relation to the assuming person, nothing would be per se understood by the union.a Nor is the relation in the assumed nature only a thing of reason, because then the union would not be real. This relation then is a real relation of inequality in one extreme, to which no relation in the other extreme corresponds at all, or at least no real relation. And so the relation is a relation of order in one related extreme; but it is not the relation of ‘caused thing to cause’, because that relation is common to the whole Trinity - nor is it a relation of ‘what is caused later to what is caused earlier’, because the Word is not anything caused; therefore it is a relation of order or of dependence that is of a reason different from all dependence in the order of caused to cause, because the relation is universally by reason of nature in one extreme.

a.a [Interpolated note] For ‘union’ is a special relation of dependence and order that is not of the same reason in both extremes: a real relation and not a relation of reason in the united nature, and a relation of inequality.

15. And although it be difficult to see that some dependence is of this sort, yet it can in some way be made clear in the case of subject and accident. For an accident has a double relation to its subject or to substance; namely of in-forming to in-formed, - and this necessarily includes imperfection in the formed subject, namely by the fact that it has potentiality with respect to ‘act in a certain respect’ (because the act is an accidental one); the other relation it has is of the naturally posterior to the prior, on which it depends as on its subject and not as on some cause (because if it has the subject as a cause, it has it as material cause, and this insofar as it in-forms the subject). If then these two relations of accident to subject are distinguished from each other, the one is necessarily a relation to the subject under the idea of imperfection in the subject, namely the imperfection of potentiality - the other, however, does not necessarily posit any imperfection in it but only natural and instantiating priority with respect to the accident.

16. Very similar to this is the dependence of human nature on the divine person, which is without any dependence of the caused on the cause; also it does not have the [divine] nature for first term but the person as it is person, such that just as the entity of nature is of a different idea and of something different from the entity proper to the person as person, so dependence on this sort of being and on that is of a different idea and of a different thing.