I'm thinking about this issue because a number of my students have asked me whether they can cite Wikipedia in their course papers. I want to explore that question, and this post will evolve as my thinking does. At the outset, though, I should state two biases. First, I am primarily an academic writer. Thus my standard for what "counts" as knowledge is somewhat severe and somewhat limited. Second, I have recently participated in a debate about a Wikipedia entry, a debate I found to be indicative of the problems that have befallen this online encyclopedia. Thus, my notions on this topic are necessarily shaped by personal experience.
Wikipedia is indisputably an important experiment in the aggregation, evaluation, and distribution of knowledge. Among its many values, Wikipedia allows anyone anywhere a chance to contribute content, and to edit content contributed by others. The presumptive result is a marketplace of ideas where massively distributed "editors" can use simple online tools to improve entries of all types, ridding them of errors in fact, clarity, and bias. Perhaps more importantly, Wikipedia promises to transcend the primary limitation of page-bound encyclopedias through its perpetual evolution. An entry about a brand of automobile will therefore be revised almost simultaneously as news reports about that car are broadcast. In this way, Wikipedia offers fulfillment of an ancient dream: the gathering and distribution of humankind's collective knowledge beyond the limitations of production costs, physical geography, and page limits. That's the idea anyway.
In my experience as an occasional editor (a generic term for anyone who updates a single entry even just once), I find Wikipedia in its current iteration to be flawed enough to warrant serious rethinking of the entire experiment. The problem is not that "just anyone" can propose or edit an entry. I actually do believe in the "marketplace of ideas" concept. The problem is when debates about entries get wound up in discursive abscesses by a handful of partisans, along with one or two wandering passers-by who got sucked in. I've seen a few of these debates (and participated in one that was marred by particularly specious reasoning). In my observations, I have noticed that far too many Wikepedia arguments demonstrate what folks in the world of collegiate debate call "lack of clash." By "clash" I don't mean vitriol. Rather I mean close and direct engagement between two or more participants of each others' ideas. Rather than clash, many Wikipedia debates descend into a chase of moving targets: new expectations are raised without address to the achievement of previous expectations. More seriously, many of these debates collapse into ad hominem attacks and appeals to misplaced authority. Almost always, notions of good will and consensus building become abandoned when the war of egos replaces the clash of ideas.
For that reason, I insist that my students (and my own scholarly publications) cite peer reviewed materials rather than Wikipedia. Now, I should be clear that Wikipedia has its uses as a third-tier resource. Indeed, Wikipedia pages generally include this note, "Wikipedia articles should be used for background information, as a reference for correct terminology and search terms, and as a starting point for further research." Following that advice, I use Wikipedia to gather unambiguous facts, check well-known dates, and confirm common spellings -- testing that knowledge by comparing the Wikipedia entry to other sources. Moreover, I often find that Wikipedia entries include links to peer reviewed or professionally edited publications that may be appropriately cited. But until Wikipedia makes some serious changes I will be unable to conclude that its contents reflect meaningful knowledge. Initially, it seems necessary for Wikipedia to require much more specialization for its editors. Certainly anyone should be able to suggest a revision. But editors ought to demonstrate content-specific expertise before being authorized to add, edit, or remove an entry. Developing a means to reduce vandalism or "drive by editing" requires more than the assumption that more participants generate better results. Wikipedia must require genuine peer review for all its articles before it merits academic citation.
Citizendium seeks to improve upon Wikipedia's model by requiring editors to use their real names and possess some demonstrable qualifications (other than an internet connection and some free time).