εἰς ἓν αἴτιον. So elsewhere it is put, ὥσπερ μία ἀρχή, κατὰ τοῦτο εἷς Θεός. The three Persons or Subsistences are yet One God, because of the one Principle of Being whence Son and spirit derive. So the Father is said to be the ἕνωσις ἐξ οὗ καὶ πρὸς ὃν ἄναγεται τὰ ἑξῆς.