What I am writing here are the rules I go by. Textual criticism does not have explicit biblical guidelines informing it. Therefore, there are many theories out there, and my canons will not match other people’s canons. So I make no claim that this is what everyone ought to hold. Full disclosure: my canons place me in-between the critical text genealogical theory, and the majority text theory.
Preliminary considerations: I hold that all of these canons, or rules, have probabilistic force only. None of them is a “knock-out” punch. Each canon needs to be weighed in the balance with all the other canons. It will frequently happen that one canon will come into conflict with another canon in the practical application. For instance, should we go with the reading that has the best attestation, or the reading that can explain the origin of all the other readings?
Furthermore, textual criticism is both an art and a science. It is a science, because extremely detailed work is done on the age and provenance (place of origin) of manuscripts. Discovering whether the correctors were one or many is also important. Textual criticism is also an art because it requires judgment on the part of the textual critic, and imagination to come up with explanations as to why a certain reading arose. The judgment of the textual critic is an essential part of textual criticism. It is unavoidable.
I have very little respect for some of the rhetoric that flies around on the internet and in print anathematizing anyone who has a different view from the writer. There is over 90% agreement between Sinaiticus/Vaticanus and the Textus Receptus/Majority text. No doctrinal difference hangs on a textual difficulty. And yet, from the rhetoric of some, one might assume that the entire world was at stake in these questions. Textual criticism must be understood in proper proportion. Those who read the KJV have the Word of God. But so do those who read the ESV.
Lastly, no Christian should be afraid of textual criticism. “Criticism” here does not mean that we believe something is in error in the original autographs (the documents that come straight from the pen of the authors). It simply means that we compare manuscripts in order to discover the original reading. We don’t have the original autographs. Nevertheless, God has providentially preserved the text of Scripture in all ages. Textual criticism is, then, an exercise in reading in the book of God’s providence. The following canons are not in any particular order, although I will indicate which ones I deem to have greater weight than others.
1. Older manuscripts will tend to attest to an older reading. Notice the word “tend.” To say that the oldest readings are always found in the oldest manuscripts is an error. The testimony of the early church fathers, for instance (more on this later) can clearly attest to a reading that is older than the oldest manuscripts. Nevertheless, on the balance of probability, the older manuscripts have a better claim to have an older reading. This canon has strength, but it must be held with caveats.
2. Geographically diverse attestation of a reading makes its authenticity much more likely. If manuscripts from various places all have the same reading, that pushes back the origin of that reading far earlier. If a reading is only present in one geographical location, one can easily suspect that the reading arose only in that location. This canon weighs very heavily with me, maybe the most of any canon. There is one caveat here that must be mentioned, however: manuscripts could have been moved from their location of origin. An Alexandrian text might have been moved to Byzantium, for instance. Some might argue that there is an Alexandrian style of manuscript. Fair enough, but then, couldn’t the scribe also move?
3. Genealogically related manuscripts have somewhat less weight. I differ here both from those following Westcott and Hort, and from the Majority text theorists. I disagree with Westcott and Hort’s theory (manuscripts must be weighed, not counted) for the following reasons: a. It is far more difficult to prove genealogical relationships between manuscripts than is often supposed; b. cross-pollinating of manuscripts is quite possible (a manuscript from a different region could be used in correcting a manuscript, thus disrupting the genealogical “purity” of a family). I differ from Majority Text theorists in that I believe genealogical relationships among manuscripts is not impossible to show. If it can be shown, then a “family” of manuscripts would have less weight. The idea here is that the “children” manuscripts (the copies that were made) are very rarely, if ever, more accurate than the “parent” manuscript. This canon weighs less heavily with me than others.
4. The more difficult reading will tend to have a higher claim to be original. This canon is based on the theory that scribes would not make a text more difficult to understand, but they might very well be tempted to make a text easier to understand. This is plausible. However, this canon has a very important caveat: there is a limit to how difficult a reading can be, and still have plausibility. This limit does have a biblical basis: God cannot lie. In other words, a reading that makes the text come into direct conflict with other texts of Scripture cannot be original.
5. The reading that can best explain the origin of all the other readings has a better claim to be original. This is a very important canon. If one reading has a greater explanatory power than another, it is more likely original. If one reading, for instance, can explain another reading as dittography (accidental repeating of a word), whereas the second reading has no explanation for how the first reading arose, then the first reading has a greater claim to be original. This canon, however, also has an important caveat: sometimes accidents can happen in transcribing that are completely random.
6. Continuity of attestation in history means that a reading has a better claim. God would not let His Word disappear completely for centuries without attestation. However, this does not mean that unique readings of recently discovered manuscripts (such as Sinaiticus) would have to be discounted automatically. God’s providence can work in hidden ways (see the book of Esther, for instance).
7. The reading of the majority of manuscripts has a better claim to be original. This has to be balanced with the chastened genealogical principle that some manuscripts are better than others. Quality and quantity of manuscripts can both be important. It is a mistake, in my judgment, to discount the Byzantine tradition simply because its manuscripts are later. Byzantium is one of the prime locations that can attest to a geographically diverse reading. The majority cannot be ignored. Majority does have weight. However, the majority is not always correct, either. To say that the majority is always right is a logical fallacy. We do not arrive at truth merely by counting noses. Otherwise Athanasius would have been wrong. Nor is each manuscript of equal weight. Here it can be seen how precisely I line up in the middle between the critical text advocates and the majority text advocates.
8. The early church fathers can be of great weight in determining how old a reading is. In some cases, they can attest to a reading that is older than our oldest manuscripts. Irenaeus, for instance, lived mostly in the second century. We have only fragments of NT manuscripts that are older than Irenaeus’s writings. He often attests to a reading older than Sinaiticus and Vaticanus (both of which are fourth century manuscripts). However, this evidence must also be approached carefully. It can be doubtful if an early church father is actually quoting a biblical passage, and it can also be doubtful which passage the early church father was quoting. It is quite a bit easier in some writings than in others. Commentaries, of course, would be the easiest, since you already know which part of the Bible is under consideration.