"The relationship between the Fourth Gospel (FG) and the Synoptics is often treated as "three against one," evoking distorted perceptions ofJohn and the Synoptics alike. Differences between the presentations and contents of these four books contribute to the flawed assumption that the Synoptics are "historical" while John is "spiritual." However, if Matthew and Luke indeed used Mark in constructing their gospels, differences in perspective between the Synoptics and FG may be rooted primarily in differences between the Markan andJohannine traditions. There may even have been contacts between these two traditions, and perhaps some of their similarities and differences originated within this contact. Because the Johannine tradition developed in its own autonomous way, parallel to Mark, these two gospels should be considered the "Bi-Optic Gospels." Evidence for such a thesis presents itself in considering the development and origin of the Johannine material and the relationship between FG and the Synoptics."
Published in Jesus in Johannine Tradition, ed. by Robert Fortna and Tom Thatcher, Louisville: Westminster/John Knox Press, 2001, pp. 175-188 http://www.thethoughtfulchristian.com/Products/0664222196/jesus-in-johannine-tradition.aspx