One of the few things we know with certainty about any text is that we started withautographs and ended up with the manuscripts we currently have. Along theway, something happened.
To properly perform textual criticism, we have to try to reconstructwhat that "something" was. What we do from there varies, of course; wemight select a copy text, or decide to be highly eclectic, or do almost anythingelse. But, ultimately, every textual process involving two or more manuscriptsinvolves an examination of the history of readings. When we set out to reconstructthe text, we call this the process of examiningInternal Evidence.
In assessing these readings, critics evaluate the history of a passage in lightof Inherent or Intrinsic Probability and ofTransmissional or Transcriptional Probability.
To put this in a single sentence, Inherent Probability concernsitself with what the author ismost likely to have written (or what a particular critic thinks the author is mostlikely to have written), while Transcriptional Probability studies what ascribe might have done to that reading.
Intrinsic Probability is what reading, standing all by itself, makesthe most sense. Hort,in §25 of his Introduction, lists factors whichmight be considered in determining intrinsic probability: "conformity togrammar and congruity to the purport of the rest of the sentence and the largercontext; to which may rightly be added congruity to the usual style of the authorand to his matter in other passages."
To put that in something more like English, Intrinsic Probability looks atwhat the author is saying at a particular point, and tries to make sense of the variantin that context; it also looks at the author's style and outlook, and tries looks for thereading which is more typical of the way the author thinks and writes.
To take an example of the latter, there are three instances in Matthew(11:15, 13:9, 13:43) of variants on the phrase
ο εχων ωτα[add/omit ακουειν]ακουετω,"let the one who has ears [to hear] hear!"
The usage with ακουεινis typical of Mark. Matthew is much moreconcise, and appears in at least two of the cases to have intended thereading ο εχων ωταακουετω, lacking the infinitive. So intrinsicprobability argues that the shorter reading is the original.
Which brings us to Transcriptional Probability. This is what scribesare likely to have done to a particular reading.
It is interesting to note that Hort spend only three sections on intrinsicprobability, but devotes ten (§28-37) to transcriptional probability. Afterall, he notes (§28) "If one various reading appears to ourselves togive much better sense or in some way to excel another, the same apparentsuperiority may have led to the introduction of the reading in the first instance.Mere blunders apart, no motive can be thought of which could lead a scribe tointroduce a consciously worse reading in place of a better." This leadsHort to the at-first unlikely conclusion, "We might thus seem to be landed inthe paradoxical result that intrinsic inferiority is evidence of originality."
But this is not what Hort means. He explains, (§28) "Transcriptional probabilityis not directly or properly concerned with the relative excellence of rival readings,but merely with the relative fitness of each for explaining the existence of theothers. Each rival reading contributes an element to the problem which has to be solved;for every rival reading is a fact which has to be accounted for, and no acceptance ofany one reading as original can be satisfactory which leaves any other variantincapable of being traced to some known cause or variation."
Hort's suggested method, then, is to take each of the various readings, assumeit is original, and see what happens -- almost a mathematical proposition.
Let's take another Biblical example -- one I've used elsewhere, but a good startingpoint because there are three readings, which often makes the direction of thechanges clearer. The passage is James 5:7, where the Textus Receptus readsο γεωργοςεκδεχεται ...εωσαν λαβευετον πρωιμονκαι οψυμονthe farmer waits... until he recieves the early and late rain. There areseveral minor variants in this verse, but the major one is about what the farmerrecieves: does he receive υετον, rain;or καρπον, fruit; ordoes the verb lack an object?
The manuscript support is as follows:
All three readings have early support, and at this stage we are not considering the valueof the manuscripts (indeed, it is by assessing readings like this thatwe determine the value of manuscripts).Assume each reading is original. Start with rain. If it had been original,it could perhaps have been lost by accident. But why change it to fruit? Thischange makes no sense unless we assume a secondary change: if rain had beenlost, a scribe might be tempted to supply an object, and thought of the wrong one.
A similar line of logic applies if we assume fruit is original: To accountfor all the readings, we must assume a two-stage change: First fruit is dropped,then some scribe emends by adding the object rain.
But assume the original had no object. This is is as awkward in Greek as inEnglish. The temptation would be to add an object. One corrector thought offruit, a reading which did not survive well; another (perhaps more thanone) thought of rain, which is even more suitable and survived well.
Thus, transcriptional probability clearly favors the reading without an object.We adopt it as the original reading -- and we slightly raise our estimate of themanuscripts containing it, for reference in the many cases where transcriptionalprobability is not so clear.
In deciding how to weigh these sorts of probability, we again turn to Hort,who popularized the terms. Of Intrinsic Probability, he says in §25-27,"The first impulse in dealing with a variation is usually to lean uponIntrinsic Probability, that is, to consider which of two readings makes the bestsense, and to decide between them accordingly.... But the uncertainty of thedecision in ordinary cases is shown by the great diversity of judgement whichis actually found to exist.... [In] dealing with this kind of evidenceequally competent critics often arrive at contradictory conclusions as to thesame variations. Nor indeed are the assumptions involved in Intrinsic Evidenceof Readings to be implicitly trusted. There is much literature, ancient no lessthan modern, in which it is needful to remember that the authors are not alwaysgrammatical, or clear, or consistent, or felicitous.... [In] the highestliterature, and notably in the Bible, all readers are peculiarly liable to thefallacy of supposing that they understand the author's reading and purposebecause they understand some part or aspect of it... and hence, in judgingvariants of text, they are led unawares to disparage any word or phrase whichowes its selection by the author to those elements of thought present in hismind which they have failed to percieve or to feel."
Again, in §31, he says, "The value of the evidence obtained fromTranscriptional Probability is incontestible. Without its aid textual criticismcould rarely obtain any high degree of security."