Excerpt from: “Why I am not a Christian” by Keith M. Parsons
[J.W.] Montgomery’s position is that, unless it is possible to point to actual contradictions between John and the synoptics, they can be regarded as complementing each other.
From this premise we should have to suppose that—as E.P. Sanders puts it apropos of the discrepancies in the teachings:
“Jesus spent his short ministry teaching in two such completely different ways, conveying such different contents, and that there were simply two traditions, each going back to Jesus, one transmitting 50 per cent of what he said and another one the other 50 per cent, with almost no overlaps.” Hence, he adds, scholars have almost unanimously concluded that the fourth gospel “represents an advanced theological development, in which meditations on the person and work of Christ are presented in the first person, as if Jesus said them” (Historical Jesus, pp. 70-71). (Wells, 1996, pp. 103-104).