So either St. Thomas Aquinas didn’t recognize this glaring contradition within the very same Question of the Summa, or your interpretation of the terms is incorrect. Considering the fact that all tradition before and since has made the same distinction and emphasis as Aquinas, I would submit that it is your interpretation of the terminology that is in error, and it is not a contradiction in his argument.
Peace and God bless!
First, I must respectfully disagree with your reasoning in the last sentence. Certainly Tradition before Aquinas recognized, where it recognized any contribution by the Son towards the eternal procession of the Spirit at all, a distinction between the immediate role of the Father and the mediate or instrumental role of the Son, but it is not at all clear that Traditon recognized the other term of the potential contradiction, that is, the language of Father and Son spirating the Spirit “equally” and “as one principle” That idea is certainly in St. Augustine and the western theologians following him, but that is not “all tradition”. Therefore, I do not believe there is the heavy presumption against a contradiction that you attempt to lay.
And here is the contradiction, as I see it: St. Thomas clarifies in Article 4 that the Father and Son are “one principle” of the Holy Ghost in precisely the sense that they act in virtue of
one power. However, to immediately or originally spirate the HS, as the Father does, and to
mediately spirat the HS, as the Son does, cannot be one and the same power. To do something originally, and to do something mediately, are clearly two different types of actions, even if the element of time is taken out of it.
This becomes clearer when we consider what St. Thomas says in the previous article, where he justifies the use of “From the Father through the Son”. In order to respond to objections, he makes clear in the main article in what sense “through” is used:
“Sometimes, however, that which is covered by this preposition “through” is the cause of the action regarded as terminated in the thing done; as, for instance, when we say, the artisan acts through the mallet, for this does not mean that the mallet is the cause why the artisan acts, but that it is the cause why the thing made proceeds from the artisan, and that it has even this effect from the artisan. This is why it is sometimes said that this preposition “through” sometimes denotes direct authority, as when we say, the king works through the bailiff; and sometimes indirect authority, as when we say, the bailiff works through the king.”
In each of these examples, the king and his bailiff and the artisan and the hammer, the snese of “through” is that of an instrumentality, and the powers are not identical. The power of a bailiff is not that of a king; the king has his powers absolutely, and any powers the bailiff has he has
by delegation from the king. This is even clearer in the illustration of the artisan and the hammer. The power of the artisan and the “power” of the hammer are clearly not the same; the artisan has the power to pound material into shape by swinging an instrument, such as the hammer, with his arm; the hammer has the power to effect a pounding by
being swung by the artisan. The artisan’s power lies in being active, the hammer’s in being passive. It would torture language out of all recongition to say that the artisan and the hammer have “the same power”.
St. Thomas seemingly deals with this by defining the “through” relationship thusly: “Therefore,
because the Son receives from the Father that the Holy Ghost proceeds from Him, it can be said that the Father spirates the Holy Ghost through the Son, or that the Holy Ghost proceeds from the Father through the Son, which has the same meaning.”
This account of “through” (in the phrase starting “because”) could be squared with the king-bailiff analogy; “through” is used in the sense of
delegation of a power. The problem is, when a power is delegated, say from a king to a bailiff, the king and the bailiff do not
both exercise it. When king directs a bailiff, for example, to lock up a prisoner, the king does not himself proceed to lock up the prisoner, and he doesn’t go down to the dungeon with the bailiff to do it together. The whole point of the delegation is to have the bailiff do it, so the king doesn’t have to.
Much less does it accord with the artisan-hammer analogy. The artisan doesn’t give the hammer his power to swing a hammer in his arm, he gives it power to form a shape
by swinging it himself.
Notice also that this account of the Father “giving” His power of spiration to the Son is incompatible with St. Thomas’s description of the Spiration in Article 4, reply to objection 1: “But if we consider the “supposita” of the spiration, then we may say that the Holy Ghost proceeds from the Father and the Son, as distinct;
for He proceeds from them as the unitive love of both.”
This description, of course, is taken from St. Augustine. The problem is it requires that Son’s power of spiration be the Son’s love for the Father. However, the Son can’t receive that from the Father; He can receive the Father’s love
for him, but He can’t receive what must be His own free action. Furthermore, the Son’s love for the Father cannot be the same as the Father’s love for the Son, so they can not be one and the same power, as is required for “as from one principle”.
I will elaborate further when I have the time, but I think I have laid out a good argument that Aquinas’s attempt to reconcile a procession “from Father and the Son as one principle” and “From the Father through the Son” is not successful. I look forward to your considered response to it. Joe