ABSTRACT
Tort cases often hinge on whether the defendant behaved ‘unreasonably’. Tort theorists have long debated what makes behavior unreasonable, with many seeking answers in economic theory or Kantian philosophy. But the question of whether a tort defendant’s conduct was reasonable or unreasonable is typically a question for the jury. And we know very little about whether lay jurors’ understanding of (un)reasonableness aligns with tort theorists’ perspectives.
This Article addresses this gap in our knowledge, experimentally examining the extent to which economic theory and Kantian theory capture how laypeople (like jurors) judge reasonableness. Specifically, this Article identifies and then tests competing economic and Kantian views about the relevance of the various inputs in the well-known Hand Formula (B < PL): the burden of taking additional precautions (‘B’), the increased probability of harm occurring in the absence of those precautions (‘P’), and the expected cost to society of the harm should it arise (‘L’).
Across five experiments, 1,046 participants read simple tort cases that included full information about B, P, and L, in plain language, and then judged whether the defendant acted unreasonably. Participants found defendants’ conduct more unreasonable when B was less than PL, as one would expect if participants engaged in some degree of Hand-style, economic balancing of costs and benefits. But, critically, information about P and L had additional, Hand-independent effects on participants’ judgments: Participants found defendants’ conduct more unreasonable as the value of PL – and particularly the value of P – increased, whether B was less than PL or not. A purely economic view of (un)reasonableness cannot explain these findings. Lay judgments, it seems, are influenced to a degree by cost-justification, but they are also influenced by Kantian consideration of the significance of risks. My results provide the first experimental evidence that Kantian views capture aspects of lay reasonableness judgments, illuminating that P, in particular, plays an outsized role in those judgments.
In short, the Hand Formula’s inputs do not have equal weight in decisionmakers’ minds. P is most influential, though decisionmakers may not be conscious of its outsized influence. These findings have significant implications for tort theory and for everyday tort practice.
Jaeger, Christopher Brett, The Hand Formula’s Unequal Inputs (February 3, 2025).
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