"I am trying to suggest how Christian Trinitarian logic has a mediating structure which is not dialectical. The key point here (simply to state things baldly for the present, without argument) is that that which lies “between” two poles is paradoxically “extra” to those two poles, an irreducibly hypostatic third. In the case of the infinite Trinity, this extra is itself indeed the procession of the love that lies between Father and Son (as Augustine put it)—yet the arriving externality of this thirdness is still guaranteed by the fact that Father and Son (according to the logic of substantive relation, perfected by Aquinas after Augustine) are in their mutually constitutive relationship only through this additional constitutive relationship to the Holy Spirit—which is not so much their “child” as the very womb of desire of truth in which the Father has originally conceived the Word of reason. If, to speak by geometrical analogy, Father and Son are points only because they are the two ends of one line, then this line is a line only because it is the base of a square whose remaining space is the Holy Spirit."
- John Milbank, The Double Glory, or Paradox Versus Dialectics, in The Monstrosity of Christ, p. 147