In the comment section to the previous post, criticism is leveled against Alands' classification of manuscripts, including a reference to Bart D. Ehrman, "A Problem of Textual Circularity: The Alands on the Classification of New Testament Manuscripts," Biblica 70 (1989): 377-88. (Read more about Aland's classification at http://www.skypoint.com/~waltzmn/MSCategories.html.)
Now my question is: how can we avoid textual circularity when considering external criteria?
When text-critics speak of "external evidence" they usually consider the textual character of a witness among other things (date, geographical distribution, etc). The evaluation of the textual character (among other things) involves a process of weighing internal evidence at as many points of variation as possible, in order to find out about the overall quality of a witness, i.e. the external evidence. The external evidence is then applied again to individual problems. It seems impossible to avoid a circular reasoning, but the question is how to best control the procedure and make it as objective as possible.
Gerd Mink describes the method currently being developed and implemented at the INTF in Münster in his article "Problems of a Highly Contaminated Tradition: The New Testament. Stemmata of Variants As a Source of a Genealogy for Witnesses,” in Studies in Stemmatology II (ed. Pieter van Reenen, August den Hollander and Margot van Mulken; Amsterdam: John Benjamins, 2004), 13-85.
"An overall hypothesis can therefore only be acquired through approximation and iterative revision of all the intermediate results. I am referring to the circular reasoning which cannot be entirely avoided in textual criticism, but has to be controlled" (p. 46).
"In other words: witnesses are good because of their good variants, variants are good because of their good witnesses. This circle cannot be avoided, but it has to be controlled. We need a method, therefore, which can provide an overall view of the consequences of all the decisions we take, so that also the overall plausibility of what we are doing can be examined. In the present method [Coherence-Based Genealogical Method] this is done through an iterative process, especially designed to perform this examination" (p. 25).