A brief application to the larger question of the trustworthiness and harmony of the Gospels may perhaps be advantageously made here. Various tendencies in the history of the harmonization of the Gospels may be recalled. One tendency, that is both conservative and simple, has been to join divergent features and to seek to weave them together into a harmonious whole. Where, however, the divergent elements are exceedingly difficult to combine in that way, it is insisted that the narratives must be regarded as reporting different events or different sayings. This approach is indeed one that I regard as fundamentally unobjectionable in principle; and at times its application leads to satisfactory results. And in general it certainly is to be preferred to the tendency, which seems to be characteristic of many modern writers, to cry "discrepancy!" at the presence of even minor linguistic differences. Or in the same spirit it may be declared dogmatically, without the benefit of any objective evidence, that two highly divergent narratives or records of teaching necessarily must be envisioned as the result of radical editorial modifications of a single source. Nevertheless, there is, in my judgment, a sounder attitude to most problems of harmonization than that which was characterized above as conservative and simple. It is marked by the exercise of greater care in determining what the Gospels as a whole and in detail actually say as well as greater restraint in arriving at conclusions where the available evidence does not justify ready answers. In particular, there is the possibility of genuine progress if one does not maintain that the trustworthiness of the Gospels allows the evangelists no liberty of composition whatsoever, and does not insist that in reporting the words of Jesus, for example, they must have been characterized by a kind of notarial exactitude or what Professor John Murray has called "pendantic precision." Inasmuch as this point seems constantly to be overlooked or disregarded in the modern situation it may be well to stress again that orthodox expositors and defenders of the infallibility of Scripture have consistently made the point that infallibility is not properly understood if it is supposed that it carries with it the implication that the words of Jesus as reported in the Gospels are necessarily the ipsissima verba. What is involved rather is that the Holy Spirit guided the human authors in such a way as to insure that their records give an accurate and trustworthy impression of the Lord's teaching.
from page 109-110, Origins of the Synoptic Gospels