One of the things I find interesting about the recent arguments on the Killian memos is the sort of argument for the conclusion of forgery that was manifested. It was, if you did not keep a close eye on it, rather difficult to follow because 1) it was in motion; 2) it was distributed.
I think we can see the argument by thinking about it in terms of its exploratory frontier. This (continually changing) frontier consists of the arguments and counter-arguments that are currently in play at a given time, each of which functions as a sort of vector. Unopposed, the vector moves the argument forward; met with an opposing vector in a counter-argument, the argument on that point can be stalled or moved in the opposite direction. Throughout much of the past week, new vectors have been added by both sides (with the side arguing that the memos were forgeries massively outpacing their opponents in laying down new vectors, both completely new vectors and vectors designed to neutralize their opponent's vectors). At the edge of the frontier there's considerable floundering on both sides - both sides are struggling to find a good formulation of what they are trying to say, both are trying to filter out misinformation, both are trying to correct their misunderstandings of the facts, etc. Things get tried out and discarded because of objections; other things endure objections to move the frontier forward (whichever direction one might consider 'forward' to be).
This is complicated by the fact that the argument was highly distributed: in other words, there was no one place you could go to find "the argument"; it was a complicated argument whose basic points were scattered among many different sites. To some extent the problems arising from this were neutralizing by establishing nodes of information that turned the scattered distribution into an argumentative net: e.g., some weblogs did very high-quality postings on particular issues in the argument and became heavily linked to because of it; some did a bit of metablogging and kept track of news; others did simple communication, notifying readers of their sites as to new elements they had found. Nonetheless, it's still the case that pinning down the precise argument and how it fit together became very complicated very quickly. Nonetheless, the elements of the argument did hang together, in great measure because of the information nodes; one of the major mistakes made by critics of the forgery claim was that they did not recognize the distributed character of the argument, and therefore treated each element as if it were an element of its own. (Another mistake, I think, was that they failed to recognize that the supporters of the forgery claim were developing their arguments by assimilating new information.)
The argument was able to be distributed because it was not deductive. I suppose one way to characterize it would be as an eliminative argument, although that makes it sound (given the restricted way in which we normally use the label) as if it were somehow an argument from ignorance rather than an attempt to marshal positive evidences in favor of one conclusion to the exclusion of the others. So my recommendation is that we call this sort of argument a "circumscriptive search" or "search by cumulative circumscription": it is an argument that uses positive considerations in a cumulative way to "zero in" on one solution.
(Incidentally, were I to give an award for the most unforunate post on the argument(s) from someone who should know better, it would have to go, alas, to this post by Brian Weatherson at "Crooked Timber." First, the particular element of the argument he is discussing is clearly not deductive; why Weatherson thought it could only be interpreted as a deductive argument, and therefore charged with a deductive fallacy, is beyond me. Second, the particular element is clearly only one element in what is a more extended argument; evaluating the element requires placing it in the context of the larger argument, which Weatherson does not do. Third, by his own lights he doesn't translate the argument correctly, because he drops the 'virtually' from the translation (and then - and here I must assume that I am just missing something in his reasoning - criticizes the argument for it?!). Fourth, even on the assumption that the argument was intended as a deductive argument, this is not a freshman logic class. When we find arguments that apparently commit formal fallacies in the real world, we need to consider the possibility that they are enthymematic, i.e., that they only appear to commit the fallacies because of a premise that is not explicitly stated. This Weatherson doesn't seem to do, either. This is all quite unfortunate, because Weatherson is a top-notch mind; he could do better.)
For an exercise in seeing how this distribution of the elements of the arguments works, see how the argument starts fitting together by looking at this small, incomplete sample of some significant nodes in the argument (listed in no particular order):
* CBS Killian Document Index at "Little Green Footballs"
* CBS Against the World at "blogicus"
* Typographic Problems with the Bush Memos at "Digitus, Finger, & Co.
* The IBM Selectric Composer at "The Shape of Days"
* Flounder.com (non-blog node)
* Power Line (several different blog posts, all of them very influential; start at September 9)
And some of the counter-vectors (which respond to, and have responses, among some of the above):
* Bush's Exam Doc -- Real or Fake at PC Magazine (non-blog node)
* TANG Typewriter Follies; Wingnuts Wrong at "Daily Kos"
* IBM Executive Typewriters at "Amygdala"
* and, of course, CBS News (lots of links; non-blog node)
The complicated character of the discourse is almost enough to give one a headache. And yet, if we think about it, this exploratory frontier, focused as it is on one particular issue and occurring in a very accessible medium, is very small and simple compared with many of the cooperative distributed arguments we deal with as a society. In my view, this is an issue that needs to be considered at greater length by philosophers and others who do work on the use of argument in social discourse.