Tertullian · a new plain-English translation from the original language
So he is one or the other, Father or Son -- daylight and darkness are never the identical thing, nor can the Father be reckoned identical with the Son, as though the pair collapsed into a single being who is simultaneously its own opposite -- which is exactly what those most vacant of men, the Monarchians, are after. He fashioned himself, on their telling, into his own son. Yet begetting runs from a father toward a son, and a son back toward a father: things that arise reciprocally from each other can never arise from themselves alone, so that a father might turn himself into a son for his own benefit, or a son set himself up as father to himself. Whatever arrangement God laid down, he himself abides by. A father cannot be a father without possessing a son, nor a son a son without possessing a father. Yet possessing something and being that thing are two separate matters: take, for instance, my being a husband -- that requires possessing a wife, and I could hardly serve as my own wife. In the same way, my being a father requires possessing a son -- I cannot double as my own son; and my being a son requires possessing a father -- I cannot double as my own father. These relations are what constitute me as what I become: possess them, and I become something -- a father through possessing a son, a son through possessing a father. But should I myself try to occupy one of these roles outright, I forfeit the very thing possession requires -- no longer a father, since I have become the father myself, nor a son, since I have become the son myself. To the extent that I must have the one and be the other, to that extent, if I were to be both, I would not be the other so long as I do not have it. For if I myself am to be the son who is also the father, I no longer have a son, but am myself the son. But not having a son while I am myself the son, how shall I be father? For I must have a son in order to be father: I am therefore not a son, since I do not have a father who makes a son. Likewise, if I myself am the father who is also the son, I have lost any father to possess, since I have become the father in my own right. But not having a father while I am myself the father, how shall I be son? For I must have a father in order to be son: I shall not, then, be father, since I do not have a son who makes a father. This will be the whole cleverness of the devil: to exclude the one by the other, while, shutting both up into one under the pretext of monarchy, he makes neither of them actually had at all -- so that there is no father, since plainly he has no son, and no son, since equally he has no father: for while he is father, he will not be son. This is how they hold their 'monarchy' -- by containing neither father nor son. 'But nothing is difficult for God.' Who does not know that? And who is unaware that things impossible with the world are possible with God? And 'God picked out what the world counts foolish, so as to put its wisdom to shame.' We have read the whole of that. Therefore, they say, it was no difficulty for God to make himself both father and son, against the pattern he handed down for human affairs: for it was no more difficult for God to make a barren woman bear, against nature, than a virgin. Granted, nothing is difficult for God: but if we use this maxim so recklessly in our presumptuous arguments, we shall be able to invent anything at all about God, as though he had done a thing simply because he could have done it. But it does not follow that, because he can do all things, we must therefore believe he has done even what he has not done -- rather, we must ask whether he has done it. God could, had he wished, have equipped man with wings for flying, as he granted to kites: yet it does not follow that, because he could, he did so at once. He could likewise have wiped out Praxeas and all the heretics together on the spot: yet it does not follow that, because he could, he did. For kites had to exist, and heretics had to exist -- and the Father had to be crucified. On this reckoning there will indeed be something even difficult for God: namely, anything he refrained from doing -- and that refusal comes not from incapacity but from unwillingness. For with God, to be able is to will, and to be unable is to be unwilling: and what he willed, he both was able to do and showed that he did. So then -- 'because if he had willed to make himself his own son, he could have,' and 'because if he could have, he did' -- you will only prove that he both could and willed it, if you first prove that he actually did it.