Development of the New Testament canon a novelty in Irenaeus's time. "Against Heresies" 3.11.7 acknowledges that many heterodox Christians use only one gospel while 3.11.9 acknowledges that some use more than four. The success of Tatian's Diatessaron in about the same time period is "...a powerful indication that the fourfold Gospel contemporaneously sponsored by Irenaeus was not broadly, let alone universally, recognized." Irenaeus apparently quotes from 21 of the New Testament books and names the author he thought wrote the text. He mentions the four gospels, Acts, the Pauline epistles with the exception of Hebrews and Philemon, as well as the first epistle of Peter, and
New Testament including works composed well into Late Antiquity, are relegated to the so-called New Testament apocrypha. Although not considered to be inspired by God, these "apocryphal" works may be helpful in the study of the New Testament in that they were produced in the same ancient context and often using the same language as those books that would eventually form the New Testament. Some of these later works are dependent (either directly or indirectly) upon books that would later come to be in the New Testament or upon the ideas expressed in them. There is even an example of a pseudepigraphical