In his introduction to the De Trinitate, Augustine stated his plan, as we saw in the first article, of beginning by establishing what he calls the initium fidei, the starting-point of faith, which he does by showing that the mystery is revealed in Scripture; and then of going on to give reasons for—reddere rationem, which is better translated, perhaps ‘to account for'— the one true God being a Trinity, and for the rightness of saying that Father, Son, and Holy Ghost are of one substance or essence. It has been commonly held that the first part of this programme occupies Bks I-VII, in which the dogma is discussed, and that the second part is undertaken in Bks VIII-XV, in which Augustine is thought to look for a sort of proof of the mystery in the created image of the Trinity which is man.