6 It may however be thought that the account here given of the hypostasis does not tally with the sense of the Apostle's words, where he says concerning the Lord that He is “the brightness of His glory, and the express image of His person,” for if we have taught hypostasis to be the conflux of the several properties; and if it is confessed that, as in the case of the Father something is contemplated as proper and peculiar, whereby He alone is known, so in the same way is it believed about the Only-begotten; how then does Scripture in this place ascribe the name of the hypostasis to the Father alone, and describes the Son as form of the hypostasis, and designated not by His own proper notes, but by those of the Father? For if the hypostasis is the sign of several existence, and the property of the Father is confined to the unbegotten being, and the Son is fashioned according to His Father's properties, then the term unbegotten can no longer be predicated exclusively of the Father, the existence of the Only-begotten being denoted by the distinctive note of the Father.
Source: Letters (New Advent)