Courts have cited Wikipedia over 300 times, and many of those cites are in my view just fine when the citation is for a tangential and uncontroversial matter. But the Seventh Circuit's use of Wikipedia in Rickher v. Home Depot, Inc., handed down Monday, strikes me as troubling.

The key issue as to one part of the plaintiff's lawsuit was the definition of "wear and tear." The plaintiff cited Webster's II New College Dictionary and Random House Webster's College Dictionary, which defined the term as "Depreciation, damage, or loss resulting from ordinary use or exposure" and "Damage or deterioration resulting from ordinary use; normal depreciation," But the court disagreed:

Although it is true that dictionary definitions of "wear and tear" often employ the word "damage," that does not mean that damage and "wear and tear" are synonymous. Wear and tear is a more specific phrase that connotes the expected, often gradual, depreciation of an item. See Wear and Tear, http://en.wikipedia.org/wiki/Wear_and_tear, last visited May 30, 2008.

It is a form of depreciation which is assumed to occur even when an item is used competently and with care and proper maintenance. For example, friction may erode a hammer's head. In the normal use of a hammer for its designed task erosion is impossible to prevent, and any attempt to eliminate this erosion would make the hammer useless. At the same time, it is expected that the normal use of a hammer will not break it beyond repair until it has gone through a certain amount of use.

A subtle difference, but one the Seventh Circuit thought to be quite important, and that does indeed appear to me important to the course of litigation. (The question in this part of the lawsuit was whether Home Depot's Damage Waiver rental contract provision — for which one had to pay more money — added anything beyond what Home Depot already provided for no extra charge under its Wear and Tear provision. If "wear and tear" was roughly synonymous with "accidental damage" but not through "misuse or abuse," then the Damage Waiver might be seen as pointless, and offering it for money might then be seen as a deceptive business practice under Illinois law. If the "wear and tear" was a narrower term than "accidental damage [without] misuse or abuse," as the court concluded, then the Damage Waiver would give the customer something, and offering it for money wouldn't be a deceptive practice.)

Now I strongly suspect that the judges cited the Wikipedia entry because it fit their preexisting understanding of what the phrase meant (an eminently reasonable mode of procedure for citations generally), so I doubt they relied on Wikipedia's wisdom to form their conclusion. Still, the parties obviously disagreed about the matter. The plaintiff's proposed definition was supported by dictionary entries (albeit shorter ones, which might have omitted important nuances). If the judges wanted to argue based on their experience, based on logic, or based on contrary lexicographic authorities — including, for instance, the use of the phrase in other sources — that's fine, and they did that in some measure. But they cited Wikipedia as the lead authority supporting their conclusion, and as the source for their important and controversial definition; and this strikes me as troubling.

First, there does seem to me to be a serious risk of manipulation by the parties in this sort of situation. The quoted part of the definition was added on Aug. 31, 2005, when the case was in progress at the district court. I have no reason to think that the change was made by anyone associated with the litigants (and the Wikiscanner check reveals nothing tell-tale, even when I check all changes from that IP address), but neither can we be sure, I think, that no such manipulation took place. And while it's important not to overestimate the risk of manipulation here — as I pointed out, the judges are likely relying on Wikipedia to support their preexisting understanding of this quite common term, rather than as an expert source that would provide such an understanding — there does seem to be some danger here. It seems possible that the judges, who after all quoted the definition as authoritative, would indeed be influenced by nuances of the definition even if they already agreed with the definition's main thrust.

And, second, I don't see much reason to see why, even unmanipulated, Wikipedia should be a substantial authority here. We don't know who wrote the definition, so we can't rely on his knowledge. This doesn't seem likely to be the sort of definition that would attract a great deal of attention and review in case of error, so that we can rely on a possible "wisdom of crowds." Dictionaries and encyclopedias aren't perfect, and I know there are arguments that Wikipedia is on balance roughly as accurate as the Encyclopedia Britannica (as well as arguments in response). But it does seem to me that, at least until such rough equivalence of Wikipedia and other sources is further demonstrated, courts should rest their decisions about important and controverted matters on sources — such as dictionaries, technical dictionaries, or encyclopedia entries — that at least have some more indicia of likely expertise.

Again, I should stress that for tangential and uncontroversial matters, Wikipedia may be quite good enough. Federal employees' time isn't unlimited, and tracking down authoritative sources to demonstrate the colorfulness of Polish boxer Andrew Golota (to give an example from another Seventh Circuit case, which cited Wikipedia to support such an assertion) is probably not the best ways to spend that time. But for something like the controversy in this case, I would think that the lead authority should be something other than a Wikipedia entry.

For some earlier thoughts of mine on Wikipedia and court opinions, see here. Thanks to my friend Steve Newman for the pointer to the Rickher case.

UPDATE: Link fixed, with thanks to Ted Frank.