The Relation between Counterfactual ("but for") and Causal Reasoning: Experimental Findings and Implications for Jurors' Decisions

BARBARA A. SPELLMAN [*] ALEXANDRA KINCANNON [**] I INTRODUCTION People often try to discover the causes of the events around them: Why did their child behave a certain way? Why did their football team lose? Why does their computer crash at critical moments? People also often trust other people to make causal decisions for them. We allow scientists to tell us that smoking causes lung cancer and that eggs are bad for us (some years, anyway). We also allow, or rather we require, jurors to make decisions about causality in many kinds of cases. Another kind of reasoning people do is to imagine the world other than it is and play out the consequences. For example, if the child had not watched so much television, if the quarterback had not thrown that interception, or if grandfather had quit smoking, might the world be a happier place? This kind of reasoning is called "counterfactual reasoning." In its most common guise, people imagine an early event ("antecedent") as being different (for example, no interception), leading to an outcome ("consequent") that may also be different (for example, winning the game). A. Counterfactual Reasoning as "but for" Causal Reasoning in the Law The legal system often asks jurors to use counterfactual reasoning to make decisions about causation. Obviously, the idea of causality is essential in law: Generally, we do not wish to punish or impose liability on someone unless he or she caused the damage at issue. Both criminal and civil codes (especially in the context of negligence) spend many pages defining what it means to be a cause. In both kinds of cases, to be considered a cause, the potential cause in question must fulfill two requirements: It must be a "but for" cause (also called "cause in-fact" or "factual cause or sine qua non") of the outcome; and it must be a legal cause (also called "proximate cause") of the outcome. The legal cause requirement limits the infinite number of "but for" causes to those for which it makes sense to hold people liable. The definition of "but for" cause can be seen in the Model Penal Code ("MPC"), the Restatement (Second) of Torts, and in common civil jury instructions. In the MPC's general definition of "causal relationship," the "but for" requirement is stated as follows: Conduct is the cause of a result when: (a) it is an antecedent but for which the result in question would not have occurred...[1] In negligence cases in California, the Book of Approved Jury Instructions ("BAJI") recommended the following "standard" jury instruction for many years: A proximate cause of injury is a cause which... produces the injury and without which the injury would not have occurred.[2] Thus, jurors' causal judgments require counterfactual reasoning and a finding that changing the antecedent would have changed the outcome in question. B. Present Questions The legal system obviously assumes that people can reason counterfactually by making this type of reasoning essential for judgments of causation. What does the psychological literature say about people's capacity for counterfactual and causal reasoning and the relation between them? This article describes the existing body of psychological research on counterfactual and causal reasoning. It then focuses on research dealing with two specific questions regarding their relation that is relevant to legal causal judgments. First, is counterfactual reasoning really the basis for causal judgments? We show how psychology's answer to that question has changed over time, and present research involving cases of multiple sufficient causes that demonstrates that counterfactual reasoning cannot, in fact, be the basis for all causal judgments. Second, in what way does counterfactual reasoning affect causal reasoning? We review research that shows that making a counterfactual judgment can affect later causal judgments; we then make suggestions as to when and why it does so--and should do so. …