Dr. E. A. Abbott, in his _Corrections of Mark_ (London, 1901) gives an exhaustive list of the deviations from Mark in which Matthew and Luke agree. Many of these are such as to suggest that Matthew and Luke used not an Ur-Marcus, but a text of Mark later than the one that has come down to us. E.g., in twelve instances Matthew and Luke agree in supplying the subject or object which our Mark omits. In fifteen, they agree in correcting abrupt constructions, supplying a connecting word. In thirteen (exclusive of [Greek: legei]) they agree in correcting Mark's historic present. In twelve they agree in replacing Mark's relative clause or his subjunctive by a participle. In twenty-three they agree in substituting [Greek: eipen] for [Greek: legei]. In thirty they agree in the use of [Greek: de] for [Greek: kai]. It is not impossible that Matthew and Luke, independently bent on improving Mark's style, have accidentally agreed in making these same improvements in the same places (especially since there are other improvements of the same sort in which they do not agree). But it is a much simpler and more adequate hypothesis, that they both used a text of Mark in which these corrections had already been made.
Yet even of this text they probably did not use the same identical copy. And as the copy used by one or both of them may have been two or three removes from the text from which it started, many changes may have crept into the copy used by one of them, not contained in the copy used by the other. This would account alike for the agreements in deviations from our present Mark, and for the fact that these corrections are not all of them found in both Matthew and Luke. This last item is further accounted for by the freedom of Matthew and Luke in making their own corrections in the copy that lay before them.[66] Allowance should also be made for the fact that we cannot be sure that we have yet recovered the true text of either Matthew or Luke.[67]
2. The agreements of Matthew and Luke against Mark can further be accounted for by the hypothesis of assimilation. Matthew made certain changes of his own in the wording of Mark; Luke apparently made many more. The various texts still extant show many efforts of copyists to bring the deviations of Matthew and Luke in small verbal items into an agreement. If this same process went on during the period covered by our earliest manuscripts, it is probable that it went on to a much greater extent at an earlier date, before our Gospels had acquired the sacredness which they later came to possess. A fine illustration of this process and its results is to be seen in the Matthean and Lucan versions of the Lord's Prayer, in which the probably original "Let thy Holy Spirit come upon us and purify us," of Luke, has been assimilated to "Thy kingdom come," and in many manuscripts also to "Thy will be done as in heaven so upon earth," of Matthew. The extent of this sort of assimilation can never be determined; but it seems quite sufficient to account for agreements of Matthew and Luke against Mark not easily accounted for on other grounds.