In its simplest manifestation, source criticism is the study of a text with an effort to determine the sources used by the text’s author. The decisive evidence for the use of sources in the New Testament lies in the New Testament documents themselves. In some cases the alleged sources consist of other texts that are available to us, while in others the possible sources are hypothetical.
The Methods of Source Criticism
The search for sources is an easier and much less speculative enterprise when the critic has several parallel traditions to analyze. Given such a situation the procedure will be:  (a) to note the evidence internal to the documents themselves, i.e. the areas of overlap and the points of difference in the different traditions. So far as internal evidence is concerned, the basic grist to the critic’s mill is the combination of agreement and disagreement in the parallel documents; in the case of the gospels this includes agreement and disagreement in wording, order, contents, style, ideas and theology. (b) To note any relevant external evidence, e.g. the statements of the early church fathers about the writing of the gospels, and (c) to propose and test different possible explanations of the evidence for comprehensiveness and simplicity. Comprehensiveness is important, since simplicity is no virtue if any substantial part of the evidence is not accounted for; but simplicity is also a significant criterion, since almost any theory can be made comprehensive if sufficient modifications and exceptions are allowed.
Source criticism may be a difficult tasks for the critics where there is only one tradition to work with. But this has not deterred scholars from making the attempt, and there are a number of supposedly tell-tale signs that the critic will look for which may indicate the use of sources. Given such a situation the critics look for possible breaks and dislocations of the sequence in narrative, stylistic inconsistency within a document, theological inconsistency within a particular passage or verse, and historical inconsistencies in a document.
Source Criticism and Synoptic Gospel
The analysis of the synoptic shows that Mark has 661 verses (vv.); Matt has 1068, and Luke has 1149. Eighty percent of Mark's material is reproduced in Matt and 65 percent in Luke. Matt and Luke have in common (in whole or in part) an approximate 220-235 vv. of non-Marcan material. Since the Synoptic having substantial similarities, questions about their relationships are inevitable. Did all three Gospel writers draw on an earlier text that is no longer extant, or is one of the three a source for the other two, or is some other explanation to be sought?
The solution to the Synoptic Problem which has commanded most support for some 50 years or more is the Two Source Theory. The two-source hypothesis holds that the similarities and divergences can be accounted for by the postulation of two written sources, one of which was the canonical Mark or an earlier written form of it, and the other a common source used by Matthew and Luke in different ways. This latter source was named Q. Marcan priority was first proposed in the 1830s, apparently independently, by Karl Lachmann and C. G. Wilke, while the full two-source hypothesis was advanced by C. H. Weisse in 1838. It was given its classic expression in an 1863 monograph by H. J. Holtzmann. The Mark-Q theory may be regarded as the basic element in modern source criticism of the synoptic gospels. But many of the variations between Matthew and Luke are difficult to account for adequately under this theory. B. H. Streeter posited the existence of two other sources in addition to Mark and Q: “M,” the material peculiar to Matthew’s gospel, and “L,” the material peculiar to Luke’s gospel. This “four-source” hypothesis was an attempt to provide a comprehensive explanation of the origin of the gospels through source criticism.
Source Criticism and John’s Gospel
The assumption that the seven miracle stories of John are derived from a special Sign Source has been widely approved. However, the size of the Signs Source is fiercely debated. Basically there are three possibilities. The first is a minimal solution, according to which the source consisted exclusively of the seven miracle stories and a limited editorial framework (John 2:11–12a; 4:54; 12:37–38; 20:30–31a). The second is a midway solution, according to which the source contained additionally some further materials like the traditional layer of John 1:35–51 and 4:1–42. Third is a maximal solution: the source additionally contained a Passion narrative so that it was a gospel resembling the Synoptics. In this case, however, John 20:30–31a cannot be claimed as the end of the source and the source itself cannot be labeled “Signs Source” any longer. As far as the theology of the source is concerned, it is difficult to see how this alleged source solved the tension between the miracles which have become much more marvelous (cf. John 11) on the one hand and Jesus’ suffering and death on the other hand.
Source Criticism and Book of Acts
It is argued that Luke has made use of traditional material in Acts, but there are evidently no continuous sources behind Acts 1–12. All attempts to reconstruct such sources have led to no convincing result. A special problem is posed by the speech of Stephen (Acts 7). The fact that it has been assigned to Stephen may indicate that Luke got to know it as an Antiochene tradition. In relation to Acts 13–28 two sources are discussed: (a) a source of the so-called “we sections” (in Acts 16; 20+21; 27–28), and (b) an itinerary source for the names of the places to which Paul came during his travels.
Source Criticism and the Epistles
Colossians and Ephesians have very close affinities; and if one assumes that at least Ephesians is Deutero-Pauline (Colossians is probably also Deutero-Pauline), one has to accept a literary dependence. Instances in favor of a direct literary dependence are phrases of Ephesians which can only be explained by assuming that they were taken over from Colossians. Colossians is therefore to be seen as the source adapted by the author of Ephesians and remolded to a great extent. Likewise, the affinities between 2 Peter 2 and Jude 4–13 (2 Peter 2:10–12, 17 with Jude 10, 12–13) are so close that a literary dependence has to be reckoned with: 2 Peter incorporated the shorter Jude; the author of 2 Peter has polished his source in parts and has omitted offensive points, such as the quotation from the apocryphal book of Enoch in Jude 14–15.
Source Criticism and the Book of Revelation
David E. Aune, R. Bauckham and A. Yarbro Collins, maintain that Revelation shares a common apocalyptic tradition with extra-canonical apocalypses due to the occurrence of formal and thematic similarities in both categories of texts. In the visions of the seven seals and of the seven trumpets there is, in each case, one larger interruption (Revelation 7; 10:1–11, 14). As an explanation for these interruptions, as well as for chapters 12 and 17, the use of sources has been assumed. It cannot be disputed that the author has made use of very different materials in many cases, but until now not even a limited agreement could be reached concerning the differing proposals. If written sources are to be assumed at all, they are of rather limited size and have been reworked intensively by the author to a degree that a differentiation between sources and orally transmitted traditions is hardly possible.
Merits and Demerits of Source Criticism
The Christian’s knowledge of the historical events that are fundamental to his/her faith derives from the New Testament, and so the study of the history of the New Testament documents is ultimately of the greatest relevance to them. It may strengthen their convictions about those events, as also their belief in the inspiration of Scripture; or it may do the opposite. One of the drawbacks of source criticism is of thinking that an author cannot be trusted where no source can be detected. The limitations of the source critic’s methods have been made clear and it cannot be assumed that it will always be possible to identify the use of written sources, still less of oral sources, especially if the author was a competent editor.
A source critical analysis allows the critic to say something about a writer’s method of writing and also about his particular interests and ideas. Since it will from time to time throw light on what the author or authors intend in a particular passage, source criticism is important for biblical exegesis in general. Difficulties of interpretation, for example, may be cleared up when a document is compared with its source and when it is seen how a tradition is used by different writers; and a source critical analysis is of obvious value to the exegete wishing to make sense of apparently divergent versions of the same tradition and wishing to avoid an arbitrary choice between the versions or an uninformed harmonization.
 David Wenham, “Source Criticism,” in New Testament Interpretation: Essays on Principles and Methods, ed. I. Howard Marshall (Carlisle: The Paternoster Press, 1977), 140-44.
 There are from time to time awkward breaks and apparent dislocations in the narrative sequence which are explicable if it is supposed that the author was trying to weave into a single account material drawn from a number of different sources. The success of the critic’s search for sources via dislocations depends on the original, author’s lack of success in integrating his sources, and will therefore be of little use if the original writer was competent as an editor. It also depends on the critic’s ability to interpret dislocations in the text accurately.
 Stylistic inconsistency within a document is a second sign pointing to the possible use of sources. For example, Luke’s birth narratives are very Hebraic; and, although a possible explanation may be that Luke was a versatile author who chose his style to suit his material, it is probably simpler to postulate the use of sources at this point, whether oral or written.
 If it can be shown that a particular passage or verse contains theological ideas that are quite untypical of, or better, still contradictory to, the theology of the writer as it is expressed elsewhere, then it may reasonably be argued either that the material is an interpolation or that it is material taken by the author from a source and not properly assimilated.
 Historical inconsistencies in a document, for example, doublets, are a fourth possible clue that may indicate that the author is using sources.
 R. E. Brown, An Introduction to the New Testament (New York: Doubleday, 1997), 111.
 In both instances so much of the order in which that common material is presented, and so much of the wording in which it is phrased are the same that dependence at the written rather than simply at the oral level has to be posited [C. M. Tuckett, “Synoptic Problem” in ABD vol.6, ed. David Noel Freedman (New York: Doubleday, 1992), 263-64].
 But what makes the synoptic problem particularly knotty is the fact that, alongside such exact agreements, there are so many puzzling differences. This combination of agreement and disagreement extends to the larger structure of the gospels as well. All three roughly follow the same order of events, even when there is no clear chronological or historical reason to do so. Each evangelist, however, omits material found in the other two, each contains unique incidents, and some of the events that are found in one or both of the others are put in a different order.
 Joseph B. Tyson, “Source Criticism of Acts,” in Method and Meaning: Essays on New Testament Interpretation in Honor of Harold W. Attridge, ed. Andrew B. McGowan and Kent Harold Richards (Atlanta: SBL, 2011), 41.
 "Q" is a hypothetical source posited by most scholars to explain what was called the Double Tradition, i.e., agreements (often verbal) between Matt and Luke on material not found in Mark. It is named probably after the German word Quelle, means ‘source. Behind the hypothesis is the plausible assumption that the Matthean evangelist did not know Luke and vice versa, and so they must have had a common source. Many cautions are necessary before Q is reconstructed. The contents are usually estimated at about 220-235 verses or parts of verses. Independently, however, both Matt and Luke omit passages found in Mark; therefore it is plausible that independently they have omitted material that existed in Q. Sometimes only Matt or only Luke will preserve material in Mark; it is also possible that material found only in one of the two Gospels might have existed in Q. We are not certain of the sequence of material in Q because Matt and Luke do not present it in the same order; nevertheless most reconstructions follow the Lucan order, since it seems that Matt worked Q material into his large sermons (For detailed study cf. Brown, An Introduction to the New Testament, 116-122; Guthrie, New Testament Introduction, 163-180).
 The basic argument for Marcan priority is that it solves more problems than any other theory. It offers the best explanation for why Matt and Luke so often agree with Mark in order and wording, and allows reasonable surmises for why Matt and Luke differ from Mark when they do so independently. For instance, neither evangelist liked Mark's redundancies, awkward Greek expressions, uncomplimentary presentation of the disciples and Mary, and embarrassing statements about Jesus. When using Mark, both expanded the Marcan accounts in the light of post-resurrection faith (Brown, An Introduction to the New Testament, 115; For a more detailed discussion of the Marcan Priority and the issues with it cf. Guthrie, New Testament Introduction, 150-163 )
 D. A. Carson & D. J. Moo, An Introduction to the NT, (Michigan: Zondervan, 2005), 94.
 In the first place, Streeter strictly limited the source Q to that material which was used by both Matthew and Luke but not Mark. In the second place Streeter called attention to the need for noting the locality from which the different earlier sources originated. Mark was the Roman gospel, Q was probably based on Antioch, M represented a Jerusalem sayings-document and L represented the Caesarean tradition, probably oral in character [B. H. Streeter, The Four Gospels: A Study of Origins (London: Macmillan, 1924)].
 Dietrich A. Koch, “Source Criticism, ” in Anchor Bible Dictionary, vols. 6, ed. David Noel Freedman (New York: Doubleday, 1992), 8403.
 It interrupts not only the continuity between Acts 6:8–15 and 7:54–60, but it is also not Lukan, as is shown by the comparison with Acts 13:17–25, where Luke develops his own contrasting view of the history of Israel. Moreover, Luke breaks off the rendering of his tradition in Acts 7:48 abruptly (cf. 17:24). It is more difficult to answer the additional question as to whether or not Luke has expanded his source by way of insertions (possibly in 7:35, 37, 42b–43). The rough transition from 7:47 to 7:48 and the possible Lukan insertions point to the use of a written source. The critical review of God’s election and Israel’s disobedience shows that the source shares the Deuteronomistic view of history, although it is probable that it was written by a (Judeo-) Christian author. (Koch, “Source Criticism, ” 8404.
 One-third of the vocabulary of Colossians appears also in Ephesians, whereas 73 of the 155 verses of Ephesians have a counterpart in Colossians. (Especially in Eph 2:1–3:19, the affinities to Colossians are very close.) Ephesians presupposes the understanding of important terms like sōma (body), kephalē (head), mystērion (mystery), oikonomia (office), peculiar to Colossians, and develops them further.
 See W. G. Kummel, Introduction to the New Testament, trans. H. C. Kee (Nashville: Abingdon, 1975, 340–46, 358–60.
 Koch, “Source Criticism,” 8405.
 See D. E. Aune, “The Apocalypse of John and Palestinian Jewish Apocalyptic,” in The Pseudepigrapha and Christian Origins: Essays from the Studiorum Novi Testamenti Societas, eds. Oegema and Charlesworth (New York: T&T Clark, 2008), 169-92; R. Bauckham, Climax of Prophecy (Edinburgh: T&T Clark, 1993), 38-91; A.Y. Collins, “The Political Perspective of the Revelation to John,” JBL 96/ 2 (1977), 241-256.
 Koch, “Source Criticism,” 8405.
 Wenham, “Source Criticism,” 146.
Brown, R. E. An Introduction to the New Testament. New York: Doubleday, 1997.
Farmer, W. R. “Modem Developments of Griesbach's Hypothesis.” NTS 23 (1977): 275-295.
Koch, Dietrich A. “Source Criticism.” In Anchor Bible Dictionary. Vols. 6. Edited by David Noel Freedman. New York: Doubleday, 1992. 8397 -8405.
Kummel, W. G. Introduction to the New Testament. Translated by H. C. Kee. Nashville: Abingdon, 1975.
Kümmel, W. G. The New Testament: The History of the Investigation of Its Problems. New York: Abingdon, 1970.
Robinson, A. T. “The Parable of the Wicked Husbandmen: A Test of Synoptic Relationships.” NTS 21 (1975): 443-461.
Tuckett, C. M. “Synoptic Problem.” In Anchor Bible Dictionary. Vols. 6. Edited by David Noel Freedman. New York: Doubleday, 1992. 8529-8539.
Tyson, J. B. “Source Criticism of Acts.” In Method and Meaning: Essays on New Testament Interpretation in Honor of H. W. Attridge. Edited by A. B. McGowan and K. H. Richards. Atlanta: SBL, 2011. 41-58.
Wenham, David. “Source Criticism.” In New Testament Interpretation: Essays on Principles and Methods. Edited by I. Howard Marshall. Carlisle: The Paternoster Press, 1977. 139-52.