Laudator Temporis Acti

Dirk Obbink, "Vanishing Conjecture: Lost Books and their Recovery from Aristotle to Eco," in Dirk Obbink and Richard Rutherford, edd., Culture in Pieces: Essays on Ancient Texts in Honour of Peter Parsons (Oxford: Oxford University Press, 2011), pp. 20-49 (at 39-40):

Those who collect fragments get used to following certain rules.

1. Don't split up integral fragments into smaller units (i.e. don't atomize the fragmentary tradition further).

2. Distinguish direct quotation from paraphrase or adaptation.

3. Pay close attention to context. Albert Henrichs has said that 'collections of fragments are both a blessing and a curse', the latter because they remove material from its original context, thus obscuring the readerly signs that signal the way it was intended to be (and obviously was) understood when it is quoted. Therefore one should not make the pericope (the amount of surrounding context to be included with a fragment or quotation being studied) too narrow. To pay attention to and when necessary to reconstruct the original context of a fragment is as important as reconstructing the original work from which it was derived, and may be our only key to it. In addition, it provides an unexpected bonus in the form of a received and in many ways new fragment.

4. You must already in a sense know what the text says before you can read or restore it. New knowledge comes by way of correction and refinement or from the new context gained. It may link to another piece of the puzzle. When William of Baskerville, the Franciscan monk and detective in Eco's The Name of the Rose, finally lays hands on the long-lost second book of Aristotle’s Poetics, he 'smiled as he read it, as if he recognized the things he expected to find'. And when questioned by the murderer Jorge as to how he knew it was the second book of Aristotle, he explains that he pieced it together from facts dropped in conversation with the murderer and knowing that these were mentioned in Aristotle's Rhetoric and the first book of the Poetics, together with a definition of comedy preserved in Isidore: 'Gradually it took shape in my mind, as it had to be. I could tell you almost all of it, without reading the pages that were meant to poison me'. Another way of putting this is, as Lionel Pearson once told me, 'You have to read the books that don’t survive before you can understand the ones that do.'

5. Never emend the text at or in a lacuna (Youtie's first law).

6. Always assume that the text makes sense. Even a corrupt one is easier to correct if you start from this principle, and even a sound text is unreadable if you don't.

5: R. Merkelbach, "Lex Youtie," Zeitschrift für Papyrologie und Epigraphik 38 (1980) 294, first named this law (iuxta lacunam ne mutaveris) after Herbert C. Youtie. See also Marco Fassino, "Sulla cosiddetta 'Lex Youtie'," Rivista di Filologia e di Istruzione Classica 126 (1998) 72-75; R. Merkelbach, "Iuxta lacunam ne mutaveris," Zeitschrift für Papyrologie und Epigraphik 142 (2003) 34; and Nikolaos Gonis, "A.S. Hunt and 'Youtie's Law'," Zeitschrift für Papyrologie und Epigraphik 151 (2005) 166. Gonis, n. 4, quotes a passage relevant to Obbink's 6th rule, from G. Levi Della Vida, "Remarks on a Recent Edition of Arabic Papyrus Letters," Journal of the American Oriental Society 64.3 (July-September, 1944) 127-137 (at 129):

Two elementary methodological criteria seem to have remained unknown to him [Karl Jahn]: first, that a newly discovered text, whatsoever its origin and character may be, must make reasonable sense, and, secondly, that its language is not expected to differ from the standard grammar and style of the linguistic area to which it belongs. To be sure, the contents of private letters are sometimes cryptic, since they often mention details which were familiar to the writers and addressees, while they remain unknown to us. However, when the things which they seem to say are absurd or meaningless, our first reaction ought to be to doubt the correctness of our interpretation rather than the soundness of their minds.

The Lex Youtie isn't included in Klaas A. Worp, "Youtie's 'Guidelines'," Bulletin of the American Society of Papyrologists 37.1/4 (2000) 111-115, but I like Youtie's penultimate guideline (at 113):

Make sure of your accents at all times. Nothing so quickly repels a Greek scholar as false accents.