In his book on editorial technique West has a very readable introduction to the various causes of textual discrepancies. What follows is a summary of a brief introduction.
Miscopying is far from being the only cause of textual variation, and misreading is far from being the only cause of miscopying. This is how West opens the section, and he proceeds with the very first way in which a text may change: the author himself may make changes after a work has already begun to circulate. Aristophanes revised
Clouds after the first production in 424/3, and both versions were around in Hellenistic times, and we have inherited the revision, according to West. The scholia to the
Argonautica quote from an earlier edition (προέκδοσις). And Ovid tells us himself that the
Metamorphoses was being circulated before he made his final revisions (Tristia 1.7.13). Besides the author, others may make conscious "improvements" to the text. This is most evident in the Greek tragedies, where the actors made changes to their copies. West says that this probably also happened to the plays of Plautus, but likely on a smaller scale, and the evidence is less clear. Slightly different is the way in which the rhapsodes handled the Homeric poems. And certain types of writing were considered open for alteration: commentaries, lexica, and grammatical works were treated differently from literary works. Also things of a technical nature, like the Hippocratic corpus, were revised or rearranged.
Changes could occur when a passage was quoted. Most of this was a result of inaccurate recollection, since ancient writers in general would quote from memory rather than unrolling a scroll and searching for a passage without the help of chapter divisions or the like. (This is not usually true of grammarians, however, who went through the trouble to look things up as a rule.) In addition, a writer might be quoting from another author or anthology, and so even when they copied directly, the passage may already have been tweaked. Quotations tend to become less accurate toward the end. And they may be deliberately altered to suit the context, such as changing γάρ to τοι at the beginning of excerpts, which happened often in anthologies, or simply filling out a line to neaten a verse.
Christian zeal could affect a text. For instance, in the Vienna ms. of Ps.-Hippocrates περὶ διαίτης, the names of Greek gods were removed, and θεοί was changed to θεός. The suppression of obscenity, however, was rarer than we might suppose according to West. In one group of mss. of Herodotus, the chapter on sacred prostitution (1.199) was omitted altogether. In one copy of Martial the copyist made changes such as
adulter for
fututor, and
turpes for
cunnos. One critic went so far as to change τῇ πιθόμην καὶ ἔρεξα in
Iliad 9.453 to τῇ οὐ πιθόμην οὐδ᾽ ἔρξα, apparently unhappy with the confession of Pheonix that he seduced his father's lover at the request of his mother.
Natural changes in orthography are an issue in the transmission of texts. The Ionian contraction of ε and ο to εο often appears as ευ in our texts. And
quoi and
quom appear often as
cui and
cum. But in Hellenistic times, there was a counter movement which tried consciously to preserve or restore original dialect forms, and this resulted in many pseudo-Ionic being placed into texts of Herodotus and Hippocrates, and pseudo-Doric forms in the bucolic poets. Planudes and his disciples regularly wrote γίγνομαι and γιγνώσκω for γίνομαι and γινώσκω. And some consistent changes are made for no apparent reason, such as in a late copy of Apollonius Rhodius, where νύμφη is used in place of κούρη.
Emendation by scholars and scribes is more evident in the Middle Ages and Renaissance than in antiquity, and is a bigger problem, according to West. Ancient conjectures are usually recorded in scholia and other commentaries, but seldom appear to have entered the textual tradition. In West's words:
the contribution of any individual must usually have been as evanescent as a pee into the river. In the Middle Ages there were fewer copies, and the scribes often had inferior knowledge of the language, so they would frequently change what they couldn't understand, and this could affect the "whole stream" or a branch of it anyway. In the copy of Lucretius from which all of our copies come, at 3.1,
E tenebris tantis tam clarum extollere lumen, the intial
E was left off on purpose, and a space provided for it where the scribe intended to return and write it ornamentally in red ink, but never got around to it.
And then there are semi-conscious or unconscious errors made in copying. Sometimes similar sounding words were mistaken, perhaps because the copyist repeated the words aloud to himself, and so words that were pronounced identically in later times could be confused, such as ἐπεὶ for αἰπὺ in Mimnermus 9.1, or εὖρον for Ἕβρον in Theocritus 7.112. The writing of
e for
ae, or
v for
b (less often the opposite), are considered cases of modernized spelling, according to West, but have the similar implications for the editor. Spoonerisms are common, for example, βαλών and λαβών, or
suscipit and
suspicit. Also, consonant clusters tend to be simplified, like ἔκλαξεν for ἔκλαγξεν, or
astersi for
abstersti.
Non-phonetic mental associations can cause unintentional changes, such as πύλαι and θύραι, which are widely found as variants. A monk might mistake a word for another that is more applicable to his life, for example, καθολκήν for καθολικήν. The copyist may unwittingly write a word or phrase that he has recently copied in place of what the text before him reads. In one copy of Hesiod
Theogony 454 the scribe has written χρυσοστέφανον for χρυσοπέδιλον, with lines 17 and 136 apparently affecting his train of thought. And in Ovid
Metamorphoses 12.103,
inritamina cornu is written as
inritamenta malorum, probably with 1.140 in mind.
Word order may be altered for various reasons, especially when the copyist has a phrase or whole line in his head while writing. One particular type of transposition is called the vitium Byzantinum, which occurs in texts of Greek tragedy, where a paroxytone is moved to the end of the iambic trimeter, making it sound more like a Byzantine dodecasyllable. In one family of Plutarch mss. the rhythm at the end of a sentence conforms to the habits of Byzantine language. Sometimes copyists try to avoid hiatus in prose by changing the word order. A more common operation is the simplification of word order: for instance, Bacchylides 15.47, Μοῦσα, τίς πρῶτος λόγων ἆρχεν δικαίων, is changed at the end to ἆρχεν λόγων δικαίων. And at Ovid
Am. 1.14.1,
dicebam "medicare tuos desiste capillos" becomes
dicebam "desiste tuos medicare capillos" in some manuscripts.
The change to more straightforward word order is one example of a wider tendency for simplification: unusual forms are replaced by more common ones; asyndeton is removed by the addition of a conjunction; things left implicit are made explicit. The copyist may be trying to fix what he thinks is a mistake, or perhaps just making the text more readable, or maybe he is simply writing what his mind expects to see there. He may mistake a note in the margin for part of the actual text. This often happens with glosses of rare words. In Hipponax fr. 72.7, ἀπηναρίσθη Ῥῆσος Αἰνειῶν πάλμυς, the rare word πάλμυς appears in only one ms. (as παλαμάς), and the others read βασιλεύς in its place.
There are mistakes of the visual type, such as haplography and dittography. Haplography is writing once what should be written twice, such as
defendum rather than
defendendum, and dittography is the opposite. Also there is the saut du même au même, which happens when the same phrase occurs more than once on the page, and the scribe, after writing the first, brings his eye back to the page at the second instance, and fails to copy what is in between.
Certain letters were confused in manuscripts, some of which I can't explain here because of the inadequacy of fonts. A few of the Greek ones are as follows, although the similarities can't be appreciated fully in computer fonts:
Α = Δ = Λ
Γ = Τ
Θ = Ο = ϲ
Η = ΕΙ
Η = Ν = Κ = Ιϲ
ΛΛ = Μ
ΑΙ = Ν
Τ = Υ
Some of the miniscules are:
α = αυ
α = ει
α = ευ
β = κ = μ
ε = ευ
η = κ
μ = ν
ν = ρ
π = σσ
The use of abbreviations caused confusion as well, and this became more common in miniscule scripts, when their use became much more common. And the lack of word division in early manuscripts was often a source of confusion, for example, Pindar
Ol. 10.55, τὸ δὲ σαφανὲς, where the rare word σαφανὲς was not easily recognized, and so this sometimes appears as τὸ δ᾽ ἐς ἀφανὲς. And a mistake like this can lead to further mistakes, such as Aristophanes
Ach. 832, where ἀλλ᾽ ἁμὶν was wrongly understood as ἀλλὰ μὶν, and then subsequently μὶν became μὴν in other manuscripts.