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Is 'But For' Causation Necessary to Establish Inducement?

The established Weatherford test for inducing patent infringement requires, as its second branch, that inducement by the indirect party be the “but for” cause of the direct infringement. This article shows that such a requirement of “but for” causation leads to problematic results, particularly when the evidence indicates that the direct infringers do not heed the encouragement provided by the indirect party. The article argues that while the “but for” causation requirement is often stated, it has rarely actually been applied, and there are several cases which suggest a less stringent requirement. This article argues that the best way to reconcile the cases is to recognize that causation in the second branch of the inducement test may be established on the basis of material contribution, rather than “but for” causation, while also recognizing that “but for” causation remains necessary for an award of any monetary remedy. This approach, combining material contribution as the substantive causation requirement at the second stage of the inducement test, with “but for” causation in awarding monetary remedies, also appropriately balances the policy concerns of ensuring effective enforcement of the patentee’s rights while avoiding the problem of overbroad enforcement.