Q source
In 2008, Matthias Klinghardt proposed that Marcion's gospel was based on the Gospel of Mark, that the Gospel of Matthew was an expansion of the Gospel of Mark with reference to the Gospel of Marcion, and that the Gospel of Luke was an expansion of the Gospel of Marcion with reference to the Gospels of Matthew and Mark. In Klinghardt's view, this model elegantly accounts for the double tradition— material shared by Matthew and Luke, but not Mark— without appealing to purely hypothetical documents, such as the Q source. In his 2015 book, Klinghardt changed his opinion compared to his 2008 article. In his 2015 book, he considers that the gospel of Marcion precedes and influenced the four gospels (Matthew, Mark, Luke, and John).