This is in direct response to blowero’s post #124, though I can’t quote pieces of it and respond in traditional fashion.
My discussion above was directed at the traditional ascriptions of the four Gospels, because that was the question you’d raised. And as noted in it, only two of the Evangelists (=Gospel writers, in this context) were among the Twelve Apostles.
The most common usage of “Apostles” in referencing New Testament figures includes 15 people: the original Twelve, noting in passing that there are variations in the lists which are traditionally considered alternate names for individuals named therein, such as Nathaniel=Bartholomew and Thaddeus=Jude; Matthias, named by lot to replace Judas Iscariot; Paul; and Barnabas. The term “apostle” is used to reference anyone sent in witness to Jesus, and is applied in passing to several other people, including a couple of women. On the other hand, “disciples” customarily means anyone identified as following Jesus during His earthly ministry, and is explicitly used of Mary Magdalene, the Bethany siblings, the seventy sent out to preach, etc. Some Protestant churches, who seem to be uncomfortable with the word “apostle,” use “the Twelve Disciples” to reference the Twelve whom He called to a special role during His ministry and who seem to be the core of the church thereafter. But note the careful capitalization distinctions I’ve made between descriptor and title for both words.
We’ve discussed the Synoptic Problem, the question of why the first three Gospels are so similar in content, at length in other threads, and higher critics are generally agreed that the texts as we have them evince a lot of borrowing between the actual compilers. Hence it’s almost certain to scholars that the Gospel of Matthew as we have it is not the work as it left the pen of Matthew Levi, if he indeed had anything to do with it. Many scholars who buy into higher or source criticism are inclined to believe the ascriptions of Mark and Luke, though some of them question whether the two Evangelists were in fact the John Mark and Luke who were the companions of Paul on his missionary journeys.
Diogenes recently did a pretty good write-up of the issue of the authorship of the Fourth Gospel, which I won’t attempt to report here. (If he or someone else who remembers it sees this thread and is so moved, I’d welcome his or another’s linking to it in a later post.) Suffice it to say that the book as it exists demonstrates a native familiarity with Greek not likely in a teenage Galilean fisherman called to discipleship and itinerant ministry, that there is a shadowy John the Elder distinct from bar Zebedee in early accounts, and that there is clear evidence of someone editing the work (Chapter 21 in particular seems to have been a later addition, as also does the famous story of the Woman Taken in Adultery).
But since you’d asked about tradition, I stuck to the traditional ascriptions – only two were Apostles among the Twelve. And those two are believed by serious scholars to have been the original inspirers and sources for the two Gospels ascribed to them, but not the authors of the two books as we have them today. And whether or not you apply “disciple” with a small “d” to the men Mark and Luke depends on how you use the term – Mark may or may not have been and Luke definitely was not a follower of Jesus during His earthly ministry, though both definitely were His followers during the early church period.