Prima - 36.3

I answer that, Whenever one is said to act through another, this preposition "through" points out, in what is covered by it, some cause or principle of that act. But since action is a mean between the agent and the thing done, sometimes that which is covered by the preposition "through" is the cause of the action, as proceeding from the agent; and in that case it is the cause of why the agent acts, whether it be a final cause or a formal cause, whether it be effective or motive. It is a final cause when we say, for instance, that the artisan works through love of gain. It is a formal cause when we say that he works through his art. It is a motive cause when we say that he works through the command of another. 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.

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Reply to Objection 4. When anyone is said to work through anything, the converse proposition is not always true. For we do not say that the mallet works through the carpenter; whereas we can say that the bailiff acts through the king, because it is the bailiff's place to act, since he is master of his own act, but it is not the mallet's place to act, but only to be made to act, and hence it is used only as an instrument. The bailiff is, however, said to act through the king, although this preposition "through" denotes a medium, for the more a "suppositum" is prior in action, so much the more is its power immediate as regards the effect, inasmuch as the power of the first cause joins the second cause to its effect. Hence also first principles are said to be immediate in the demonstrative sciences. Therefore, so far as the bailiff is a medium according to the order of the subject's acting, the king is said to work through the bailiff; but according to the order of powers, the bailiff is said to act through the king, forasmuch as the power of the king gives the bailiff's action its effect. Now there is no order of power between Father and Son, but only order of 'supposita'; and hence we say that the Father spirates through the Son; and not conversely.