I'd like to turn around KK's original post and ask is what Irenaeus said HIS OWN (i.e. Irenaeus's) methodology for grouping material common to longer gospels into MaRKaH (MARK) - i.e. Matthew, maRk, luKe and JoHn)
And he immediately goes on to say:It is not possible that the Gospels can be either more or fewer in number than they are. For, since there are four zones of the world in which we live, and four principal winds, while the Church is scattered throughout all the world, and the "pillar and ground" of the Church is the Gospel and the spirit of life; it is fitting that she should have four pillars, breathing out immortality on every side, and vivifying men afresh. From which fact, it is evident that the Word, the Artificer of all, He that sitteth upon the cherubim, and contains all things, He who was manifested to men, has given us the Gospel under four aspects, but bound together by one Spirit. As also David says, when entreating His manifestation, "Thou that sittest between the cherubim, shine forth." For the cherubim, too, were four-faced, and their faces were images of the dispensation of the Son of God. For, it says, "The first living creature was like a lion," symbolizing His effectual working, His leadership, and royal power; the second was like a calf, signifying [His] sacrificial and sacerdotal order; but "the third had, as it were, the face as of a man,"--an evident description of His advent as a human being; "the fourth was like a flying eagle," pointing out the gift of the Spirit hovering with His wings over the Church. And therefore the Gospels are in accord with these things, among which Christ Jesus is seated. For that according to John relates His original, effectual, and glorious generation from the Father, thus declaring, "In the beginning was the Word, and the Word was with God, and the Word was God." Also, "all things were made by Him, and without Him was nothing made." For this reason, too, is that Gospel full of all confidence, for such is His person. But that according to Luke, taking up [His] priestly character, commenced with Zacharias the priest offering sacrifice to God. For now was made ready the fatted calf, about to be immolated for the finding again of the younger son. Matthew, again, relates His generation as a man, saying, "The book of the generation of Jesus Christ, the son of David, the son of Abraham;"(11) and also, "The birth of Jesus Christ was on this wise." This, then, is the Gospel of His humanity;(12) for which reason it is, too, that [the character of] a humble and meek man is kept up through the whole Gospel. Mark, on the other hand, commences with [a reference to] the prophetical spirit coming down from on high to men, saying, "The beginning of the Gospel of Jesus Christ, as it is written in Esaias the prophet,"--pointing to the winged aspect of the Gospel; and on this account he made a compendious and cursory narrative, for such is the prophetical character.
And the Word of God Himself used to converse with the ante-Mosaic patriarchs, in accordance with His divinity and glory; but for those under the law he instituted a sacerdotal and liturgical service.(1) Afterwards, being made man for us, He sent the gift of the celestial Spirit over all the earth, protecting us with His wings. Such, then, as was the course followed by the Son of God, so was also the form of the living creatures; and such as was the form of the living creatures, so was also the character of the Gospel.(2) For the living creatures are quadriform, and the Gospel is quadriform, as is also the course followed by the Lord. For this reason were four principal (kaqolikai) covenants given to the human race: one, prior to the deluge, under Adam; the second, that after the deluge, under Noah; the third, the giving of the law, under Moses; the fourth, that which renovates man, and sums up all things in itself by means of the Gospel, raising and bearing men upon its wings into the heavenly kingdom.
One thing that I noticed this time reading this passage is that Irenaeus's natural order would seem to imply the last juxtaposition between the Encratites who use proto-Matthew and a group who use Mark. This is most puzzling. If you read what is said about Mark in the first paragraph about the gospel of Mark it would make sense that Irenaeus would connect this with the Paraclete given the fact that Matthew is identified as the incarnation (in other words if John takes it's starting point from Jesus in heaven and Luke with the priesthood established by God and Matthew the incarnation it would only follow that Mark represents the Paraclete because the Paraclete comes after Jesus and the fact that people are only redeemed by believing in the resurrection and thus after the Passion.These things being so, all who destroy the form of the Gospel are vain, unlearned, and also audacious; those, [I mean,] who represent the aspects of the Gospel as being either more in number than as aforesaid, or, on the other hand, fewer. The former class [do so], that they may seem to have discovered more than is of the truth; the latter, that they may set the dispensations of God aside. For Marcion, rejecting the entire Gospel, yea rather, cutting himself off from the Gospel, boasts that he has part in the [blessings of] the Gospel. Others, again, that they may set at nought the gift of the Spirit, which in the latter times has been, by the good pleasure of the Father, poured out upon the human race, do not admit that aspect presented by John's Gospel, in which the Lord promised that He would send the Paraclete; but set aside at once both the Gospel and the prophetic Spirit. Wretched men indeed! who wish to be pseudo- prophets, forsooth, but who set aside the gift of prophecy from the Church; acting like those who, on account of such as come in hypocrisy, hold themselves aloof from the communion of the brethren. We must conclude, moreover, that these men can not admit the Apostle Paul either. For, in his Epistle to the Corinthians, he speaks expressly of prophetical gifts, and recognises men and women prophesying in the Church. Sinning, therefore, in all these particulars, against the Spirit of God, they fall into the irremissible sin. But those who are from Valentinus, being, on the other hand, altogether reckless, while they put forth their own compositions, boast that they possess more Gospels than there really are. Indeed, they have arrived at such a pitch of audacity, as to entitle their comparatively recent writing "the Gospel of Truth," though it agrees in nothing with the Gospels of the Apostles, so that they have really no Gospel which is not full of blasphemy. For if what they have published is the Gospel of truth, and yet is totally unlike those which have been handed down to us from the apostles, any who please may learn, as is shown from the Scriptures themselves, that that which has been handed down from the apostles can no longer be reckoned the Gospel of truth. But that these Gospels alone are true and reliable, and admit neither an increase nor diminution of the aforesaid number, I have proved by so many and such [arguments]. For, since God made all things in due proportion and adaptation, it was fit also that the outward aspect of the Gospel should be well arranged and harmonized. The opinion of those men, therefore, who handed the Gospel down to us, having been investigated, from their very fountainheads, let us proceed also to the remaining apostles, and inquire into their doctrine with regard to God; then, in due course we shall listen to the very words of the Lord.
The difficulty is that the Paraclete only appears as a concept in John now. So there is a reference (perhaps added later) where 'the aspect of the Paraclete' is mentioned.
Moreover Irenaeus's consistent point about Mark is that the heretics separate 'Jesus' and 'Christ' through it. As Ehrman notes this might sound like an adoptionist understanding of the baptism but Irenaeus doesn't mention that. Instead he references something which isn't in Mark any more at least the idea that Christ stood watching while Jesus suffered on the Cross. While it is important to note that this alone would suggest that Irenaeus's Mark did not resemble our surviving text it is also worth noting that in Adv Haer 4.2 Irenaeus identifies another passage as being in Mark which does not currently appear in Mark.
Indeed Irenaeus goes out of his way to cite the beginning of Mark and the end of Mark (the long ending) as a way of confirming to us that (a) Mark did not separate Jesus and Christ as its original users (the heretics) suggested and (b) to reject the inferences from the long gospel of Mark which mentioned the Paraclete that the Paraclete was Christ and Jesus a distinct being. Once again it has to be assumed (unless someone can come up with a better answer) then that current text of Adversus Haereses has gone under a lot of revision. In its original form the users of Matthew were opposed to the gospel of Mark something we already see reflected in Papias. Those users of Matthew seem to be the Encratite followers of Tatian who because of their opposition to Mark and its mention of the Paraclete (at least originally) must also have rejected the Apostle Paul.
While this thread of logic might not make sense to most people it does come up elsewhere in Adversus Haereses in chapter 15 which follows and introduces Luke and Acts to the readers. Irenaeus first says 'here is Luke, you have to accept him, his gospel and Acts' and goes through a lengthy argument in favor of all three. Many read this as being directed against the Marcionites but look at the last chapter (or the beginning of chapter 16 as it is now divided):
Many of the same ideas presented here have already been introduced in the former chapter we just studied in 3.11.7:But again, we allege the same against those who do not recognise Paul as an apostle: that they should either reject the other words of the Gospel which we have come to know through Luke alone, and not make use of them; or else, if they do receive all these, they must necessarily admit also that testimony concerning Paul, when he (Luke) tells us that the Lord spoke at first to him from heaven: "Saul, Saul, why persecutest thou Me? I am Jesus Christ, whom thou persecutest; " and then to Ananias, saying regarding him: "Go thy way; for he is a chosen vessel unto Me, to bear My name among the Gentiles, and kings, and the children of Israel. For I will show him, from this time, how great things he must suffer for My name's sake." Those, therefore, who do not accept of him [as a teacher], who was chosen by God for this purpose, that he might boldly bear His name, as being sent to the forementioned nations, do despise the election of God, and separate themselves from the company of the apostles. For neither can they contend that Paul was no apostle, when he was chosen for this purpose; nor can they prove Luke guilty of falsehood, when he proclaims the truth to us with all diligence. It may be, indeed, that it was with this view that God set forth very many Gospel truths, through Luke's instrumentality, which all should esteem it necessary to use, in order that all persons, following his subsequent testimony, which treats upon the acts and the doctrine of the apostles, and holding the unadulterated rule of truth, may be saved. His testimony, therefore, is true, and the doctrine of the apostles is open and stedfast, holding nothing in reserve; nor did they teach one set of doctrines in private, and another in public.
In both paragraphs the conversation segues to the Valentinians who resemble the Encratites described here but continue to produce gospels. So the Encratites of Tatian used one gospel identified according to Irenaeus's schema as 'proto-Matthew in Hebrew' but in reality we know that they used a Diatessaron. Already Epiphanius helps make the argument for us that 'proto-Matthew (= the Gospel of the Hebrews) was the Diatessaron. But why does Irenaeus go on in chapter 15 to say to these Encratites that if you don't use Luke you won't have all these stories? I think we have by now solved the mystery. The Encratites were being forbidden in Rome and surrounding areas at least from using their preferred text. Somehow they were 'assigned' to the 'man-gospel' (= Matthew) but if they have Matthew alone they don't get this long list of stories familiar to them from their Diatessaron and only found in Luke:Others, again, that they may set at nought the gift of the Spirit, which in the latter times has been, by the good pleasure of the Father, poured out upon the human race, do not admit that aspect [of the evangelical dispensation] presented by John's Gospel, in which the Lord promised that He would send the Paraclete; but set aside at once both the Gospel and the prophetic Spirit. Wretched men indeed! who wish to be pseudo- prophets, forsooth, but who set aside the gift of prophecy from the Church; acting like those who, on account of such as come in hypocrisy, hold themselves aloof from the communion of the brethren. We must conclude, moreover, that these men can not admit the Apostle Paul either. For, in his Epistle to the Corinthians, he speaks expressly of prophetical gifts, and recognises men and women prophesying in the Church. Sinning, therefore, in all these particulars, against the Spirit of God, they fall into the irremissible sin
It would seem then that the fourfold gospel was created principally to ween the users of the Diatessaron off of their preferred gospel text. Already Irenaeus embraces Justin and fails to mention that Tatian wrote the Diatessaron. Was that because the people knew that the 'super gospel' was much older or that he recognized that he wasn't going to convince them of the recentness of its creation?Now if any man set Luke aside, as one who did not know the truth, he will, [by so acting,] manifestly reject that Gospel of which he claims to be a disciple. For through him we have become acquainted with very many and important parts of the Gospel; for instance, the generation of John, the history of Zacharias, the coming of the angel to Mary, the exclamation of Elisabeth, the descent of the angels to the shepherds, the words spoken by them, the testimony of Anna and of Simeon with regard to Christ, and that twelve years of age He was left behind at Jerusalem; also the baptism of John, the number of the Lord's years when He was baptized, and that this occurred in the fifteenth year of Tiberius Caesar. And in His office of teacher this is what He has said to the rich: "Woe unto you that are rich, for ye have received your consolation;"(6) and "Woe unto you that are full, for ye shall hunger; and ye who laugh now, for ye shall weep;" and, "Woe unto you when all men shall speak well of you: for so did your fathers to the false prophets." All things of the following kind we have known through Luke alone (and numerous actions of the Lord we have learned through him, which also all [the Evangelists] notice): the multitude of fishes which Peter's companions enclosed, when at the Lord's command they cast the nets;(7) the woman who had suffered for eighteen years, and was healed on the Sabbath-day;(8) the man who had the dropsy, whom the Lord made whole on the Sabbath, and how He did defend Himself for having performed an act of healing on that day; how He taught His disciples not to aspire to the uppermost rooms; how we should invite the poor and feeble, who cannot recompense us; the man who knocked during the night to obtain loaves, and did obtain them, because of the urgency of his importunity;(9) how, when [our Lord] was sitting at meat with a Pharisee, a woman that was a sinner kissed His feet, and anointed them with ointment, with what the Lord said to Simon on her behalf concerning the two debtors;(10) also about the parable of that rich man who stored up the goods which had accrued to him, to whom it was also said, "In this night they shall demand thy soul from thee; whose then shall those things be which thou hast prepared?"(11) and similar to this, that of the rich man, who was clothed in purple and who fared sumptuously, and the indigent Lazarus;(12) also the answer which He gave to His disciples when they said, "Increase our faith;"(13) also His conversation with Zaccheus the publican;(14) also about the Pharisee and the publican, who were praying in the temple at the same time;(1) also the ten lepers, whom He cleansed in the way simultaneously;(2) also how He ordered the lame and the blind to be gathered to the wedding from the lanes and streets;(3) also the parable of the judge who feared not God, whom the widow's importunity led to avenge her cause;(4) and about the fig-tree in the vineyard which produced no fruit. There are also many other particulars to be found mentioned by Luke alone, which are made use of by both Marcion and Valentinus. And besides all these, [he records] what [Christ] said to His disciples in the way, after the resurrection, and how they recognised Him in the breaking of bread.
Whatever the case his tactic seems to be to identify the Diatessaron with proto-Matthew (as Epiphanius does) and I would assume put forward the idea that the material that they heard in the liturgy which now appears in John, Luke and Mark were actually from separated gospels of John, Luke and Mark rather than a single long gospel.