The Sixth Circuit recently issued a decision, that, in my opinion, stretched the well-established causation requirement for copyright damages beyond the breaking point.
In Thoroughbred Software Int'l, Inc. v. Dice Corporation, No. 06-2080 (6th Cir. June 14, 2007), the plaintiff licensed software to the defendant. Under the license, the licensee was permitted to copy and install the software on end-users' computers, but had to pay a license fee each time it did so. Further copying by the defendant was prohibited. At trial, the plaintiffs proved that the defendant made several copies of the software for which it did not pay the plaintiff. Some involved software the defendant installed on end-users' computers. Some copies were never installed on anyone's computer.
The most interesting question on appeal was whether the plaintiff should have been awarded damages for the copies that were NOT installed on any end-user's computer. They were just sitting there in defendant's office, gathering dust.
The defendant argued that, since it never installed the uninstalled copies on anyone's computer, the plaintiff didn't lose any of the licensing fees provided in the license for them, so there was no damage. Sixth Circuit acknowledged that a plaintiff "must prove the existence of a causal connection" between the alleged infringement and the alleged damage. It then pointed to a 2d Circuit case where someone had used a copyrighted object in an ad campaign without obtaining permission. The 2d Circuit case held that the copyright owner should have received a reasonable royalty for the use of the copyrighted object in the ad campaign.
The 6th Circuit then stretched this holding even further (way too far, in my view), and used it as the basis to hold that the plaintiff should receive a reasonable royalty even as to the copies that were made but never used. Its basis for doing this was that it was more equitable to give something to the plaintiff for the unlawful copies than to let the wrongdoer off scot-free as to those wrongly-made copies. This would seem to make a mockery of the causation requirement, as this "principle" would apply in almost every case, causation or not.
So if you want a broad interpretation of the causation requirement, here's your authority.