The greater portion of the results of modern criticism cannot be said as yet to have attained finality, or even to have advanced beyond the stage of working hypotheses. But it is otherwise with some, the evidence for which is so strong as to render their truth almost certain, and among those theories which must be placed in this latter category is one which is of the utmost interest to Catholics, not only on account of its own intrinsic interest, but because of its obvious bearing on the nature and method of the inspiration of the Holy Scriptures.
Composition of the Gospels
This is the discovery of the fact -- for it may now justifiably be considered as a fact that is proved beyond reasonable doubt -- that the Gospels, as we now have them, are not wholly original compositions made in their entirety by those whose names they bear, but that in the course of their production use has been made of other earlier documents, which are not merely quoted or referred to, but are actually incorporated, with only verbal alterations, in the later works. This is clearly a fact of the very greatest importance, with the most far-reaching consequences in every direction, and it is accordingly to this point and to some of its more obvious consequences that I propose to confine myself in what I have to say.
Earlier Sources
The main proof of this dependence of our Gospels on earlier sources, which sources were almost certainly written sources and not merely handed down by verbal tradition, is drawn from a careful and exact comparison of the three first Gospels one with another wherever their narratives cover the same ground. There is found to be a most singular and minute correspondence between the three narratives, which sometimes amounts to actual verbal identity, extending over one or more verses in succession. Such verbal identity would afford a strong presumption that a common document had been utilised by both writers, even were we dealing with only two works which showed this peculiarity. But in that case we could not get beyond probability; there would not be sufficient evidence to admit of any certainty in our conclusions. The fact, however, that we have three writings to compare enables us to attain to a much higher degree of certainty in our conclusions, because there is so much more opportunity of making valid deductions and of checking by a further comparison the results at which we arrive. In this particular instance the problem is one of quite extraordinary complexity and intricacy, for the verbal identities which are so frequent are balanced by constant and minute divergences which are exceedingly hard to explain; but still, in spite of these difficulties, the main conclusions stand out perfectly clear, and may be regarded as proved with practical certainty.
Gospel of St Mark a "Source"
The first and third Gospels are certainly composite in origin, built up out of earlier sources, one of which sources is to be found in both cases in the Gospel of St Mark. Whether the Gospel of St Mark is itself similarly dependent on earlier documents is a question which is still keenly debated, and which need not detain us now. The important point which I wish to emphasise particularly now, and which I think you may safely regard as proved, is that the authors of both the first and the third Gospels -- those, namely, which are known to us by the names of the Gospels of St Matthew and St Luke -- had before them, and made extensive use of, a Gospel writing which was almost, if not quite, identical with our second Gospel as we have it to-day. Both of them made use of other sources besides from which to draw the facts that they record, but in each the framework upon which the whole story is built up is supplied by the Gospel of St Mark. And, of course, the fact that we can thus distinguish with complete accuracy one of the sources employed goes a long way towards the solution of the entire problem, by making it very much more easy to separate the others one from another.