Scribal Error

The most common types of alteration made by scribes to the texts that they copy are these:

Of Omission:

homeoteleuton: the scribe paused, then resumed writing but skipped ahead because of the similarity of the endings of two lines, thus leaving out a passage.

homeoarchy: eye-skip because of the similarity of the beginnings of two lines.

haplography: copying once what appeared in the exemplar twice ("pewterer" reduced to "pewter," or "that that" reduced to "that").

Of Addition:

dittography: mechanical repetition, by trick of memory ("that that" when original had only "that").

contamination: extraneous element from elsewhere appears on the page.

Of Transposition:

metathesis: reversing letters, words, phrases.

Of Alteration:

unwitting.
Unwitting mistranscription: the First Folio Anthony and Cleopatra, in V.ii.87, gives "an Antonie twas" where Shakespeare had written "an autumn twas"; the typesetter "saw" "Antonie" there, partly because the name had appeared so often already, and partly because it made "sense" in the passage, so the initial error was not immediately caught.

deliberate: the scribe acts as editor to correct and improve the original.

There are two traditional "doctrines" of textual criticism, based on the assumption that scribes always simplify and "trivialize" the author's text (cf. Lee Patterson's essay on the Kane-Donaldson edition of Piers Plowman, reprinted in his Negotiating the Past):
difficilior lectio potior: the more difficult the reading the more likely [it is to be authorial];
brevior lectio potior: the shorter the reading the more likely [it is to be authorial].
Such doctrines assume a romantic concept of the superior genius of the author.
There are currently some challenges being mounted in the way that textual critics view scribes, in the work of Jerome McGann among others, in part based upon theoretical challenges to the romantic concept of the author. Derek Pearsall summarizes, and applies to medieval English texts, some of these ideas in his "Texts, Textual Criticism, and Fifteenth Century Manuscript Production." On pp. 125-126, for instance, he notes that an editor who accepts the doctrine of difficilior lectio must deny that scribes could improve their originals. Yet the tradition of Chaucer manuscripts, among others, proves the presence in fifteenth-century manuscript production of quite intelligent editors. Further (pp. 126-127), especially with respect to the romances (Beves of Hamtoun, for instance), Pearsall declares that "each act of copying was to a large extent an act of recomposition, and not an episode in a process of decomposition from an ideal form." Rather than any sort of mechanistic application of "doctrines," then, postmodern editors will need to consider each case on its own merits.