Harnessing Adversarial Process: Proof Burdens, Affirmative Defenses, and the Complementarity Principle

Abstract

This paper studies the evidence production game in adversarial litigation, wherein litigating parties choose how much to spend amassing evidence for their side. The payoff structure of this game is such that one party strategically complements (i.e. mimics her opponent's advances and retreats) while the other strategically substitutes (i.e., does the opposite of her opponent). Which party plays which role depends on how litigation is structured. The question thus arises: should litigation be designed to induce the plaintiff to complement and the defendant to substitute, or vice versa? The paper argues that the answer depends on whether and whose primary activity incentives are being set by the particular evidentiary contest in question. Within each subsidiary evidentiary contest, the target should be induced to complement and her adversary to substitute. In some cases the defendant will be the incentive target, as when the issue is the defendant's negligence or contractual breach. In other cases, the plaintiff will be the target, as when the defendant defends by claiming that the plaintiff has been contributorily negligent or has herself failed to meet a prior contractual obligation. These results resonate with current law. (A companion paper A Primary Activity Approach to Proof Burdens applies these results to the problem of allocating the burden of proof.)