By using the two gospels as lenses through which we can perceive the refracted image of the earlier gospel tradition, we can hypothetically reconstruct its outline and many of its motifs. Although some of the material found in one gospel, but not the other, could have been part of an earlier core, and material common to both might have circulated in smaller units, and been inserted by both authors independently, the process of determining the likely core by isolating the parallel material is a justifiable method. The process is analogous to the reconstruction of Q, although there we have not just Matthew and Luke, but a third comparison point as well to tell us what Q is not, that is, Mark. In addition, while Matthew and Luke have made use of a written source, keeping fairly close to it, Mark and John have evidently utilized a much more fluid tradition, perhaps one or more oral accounts of the gospel narrative. Nevertheless, the opportunity exists here to address the question of the earlier elements of the gospel narrative tradition through a comparison of Mark and John, with intriguing results. We find that what the two gospels share-and therefore what we can postulate as a core tradition that could explain each of their developments-constitutes an entire gospel. The conclusions of this study cannot be proven, but the case for any of the possible explanations for the relationship of Mark and John must be made on the basis of the theory’s overall plausibility, in much the same way that the argument for the existence of Q ultimately convinces, or fails to convince, on the basis of its overall plausibility. The scholarly debate over whether John is dependent upon Mark has often focused on details of comparison between the two, but the most compelling arguments on both sides have tried to create a plausible theory of the whole. Just as in text criticism, where a reading is considered likely if it can explain other divergent readings, so here a hypothetical source is considered likely if it can explain two other texts.