John Cassian, Conferences I–X IX.10: Of the order of the different kinds laid down with regard to the character of prayer

And so to begin with we must consider the actual force of the names and words, and discuss what is the difference between prayer and supplication and intercession; then in like manner we must investigate whether they are to be offered separately or all together; and in the third place must examine whether the particular order which is thus arranged by the Apostle’s authority has anything further to teach the hearer, or whether the distinction simply is to be taken, and it should be considered that they were arranged by him indifferently in such a way: a thing which seems to me utterly absurd. For one must not believe that the Holy Spirit uttered anything casually or without reason through the Apostle. And so we will, as the Lord grants us, consider them in the same order in which we began.