Stepwise liability: Between the preponderance rule and proportional liability

Published date01 October 2023
AuthorShay Lavie
Date01 October 2023
Subject MatterArticles
Stepwise liability: Between the
preponderance rule and
proportional liability
Shay Lavie
Law School, Tel Aviv University, Tel Aviv, Israel
There are two familiar decision rules: the binary, preponderance of the evidence and the
continuous, proportional liability rule. This article proposes a thought experiment. Instead
of all-or-nothing or a continuous rule, the law can utilise a middle groundassigning liability
stepwise, according to the procedural progression of the casestepwise liability. Stepwise
liability relies on the gradual design of civil procedure. Under the current system, the plaintiff
has to pass several procedural thresholds with increasing evidentiary requirements in order to
proceed to trial. Examples are a motion to dismiss and then a summary judgment. I propose
that, corresponding to the procedural progression of the case, after surviving each step the
plaintiff will be entitled to a gradually increasing share of the damages. Stepwise liability offers
several advantages relative to the traditional rules. It provides partial compensation where the
defendants liability falls short of the 50% threshold, hence restoring incentives to take care.
Unlike the proportional rule, this outcome can be achieved without major modif‌ications to
the existing decision rules. Unlike both rules, the proposal enables plaintiffs to cash in with
some award before trial. I analyse the foregoing advantages together with the potential pitfalls,
such as over-deterrence, larger legal expenses, and the day-in-court ideal.
discontinuous rule, legal procedure, motions to dismiss, optimal deterrence, proportional
liability, summary judgment, the preponderance rule
There is a long-standing debate in the literature about the preferable decision rule: the discontinuous, pre-
ponderance of the evidence rule or the smooth, proportional liability rule. The former, preponderance
Corresponding author:
Shay Lavie, Law School, Tel Aviv University, Minkoff Building, #428, Tel Aviv, 6997801,
The International Journal of
Evidence & Proof
2023, Vol. 27(4) 279306
© The Author(s) 2023
Article reuse guidelines:
DOI: 10.1177/ 13657127231185887
rule assigns the victory to the plaintiff only in case it shows that her case is more probable than her rivals
(e.g., Mueller and Kirkpatrick, 2013: § 3.5). This is the default rule, at least in Anglo-American legal
systems. In probabilistic terms, it is commonly thought that the plaintiff should win according to this
rule if there is more than a 50% chance that her account is correct (e.g., Glöckner and Engel, 2013:
242). It thus presents an all-or-nothing decision rule. The latter, proportional rule allows for a partial
remedy, based on the likelihood that the evidence justif‌ies relief. Thus, a plaintiff who proves her case
at a level of x% is entitled to that proportion of the damages, whether or not the evidence surpasses
the 50% threshold.
The proportional rule thus presents a continuous decision rule, which can be con-
trasted with the preponderance rule (e.g., Abramowicz, 2001: 235236).
Each rule presents, of course, advantages and disadvantages. The most salient advantage of the propor-
tional rule concerns ex-ante deterrence, as the proportional rule, by and large, better incentivises wrong-
doers to take care, ex-ante (Pelled, 2021). To demonstrate, a wrongdoer whose responsibility, in
probabilistic terms, is always 40% will never pay for her wrongdoing under the preponderance rule
an outcome that undermines the goal of deterrence. Likewise, a wrongdoer who is responsible for 70%
will always be liable under the preponderance rule, and thus be incentivised to take excessive care. The
proportional rule avoids these pitfalls. By contrast, the preponderance rule minimises, under certain
assumptions, the erroneous allocation of remedies between the two parties, in that specif‌ic case (Kaye,
1982: 507508). More generally, the preponderance rule is our current default burden of proof rule in
civil cases(Spottswood, 2021a: 202). It better f‌its the current legal climate, where the judge has to
choose between two versions: the plaintiffs or the defendants (Pelled, 2021). Indeed, while the propor-
tional rule allegedly performs better than the preponderance rule for all kinds of cases, it faces the innate
conservatism of lawyers when considering reforms to trial procedure(Spottswood, 2021b: 824, 827).
This article contributes to the literature by presenting a thought experimentlevelling the choice
between the discontinuous, preponderance rule and the continuous, proportional rule. Instead of
all-or-nothing or a continuous rule, the law can utilise a middle groundassigning liability stepwise,
that is, a stepwise liability rule. In particular, the proposed middle rule is tied to the procedural progres-
sion of the case. To demonstrate, with each procedural step that the plaintiff passessay, motion to
dismiss and then summary judgmentthe defendants liability jumpssuch that the plaintiff will be
able to drop and cash in with a higher share. Thus, the proposal can correct some of the diff‌iculties
with the current rules. In particular, stepwise liability enables partial compensation where the defendants
liability falls short of the 50% threshold, hence restoring incentives to take care (think about cases in
which plaintiffs survive a motion to dismiss but should fail at trial). Unlike the proportional rule (and
hybrid rules that the literature has proposed), this outcome could be achieved without requiring the fact-
f‌inder to announce a probabilistic number. Thus, it better f‌its the role of judges in our system and neces-
sitates little modif‌ications in the existing legal landscape.
Stepwise liability, then, harnesses the gradual design of the legal process to achieve an outcome that
resembles in some respects the proportional rule. Nevertheless, stepwise liabilitys effects are by no
means identical to the proportional rule. It does not merely suggest jumpsin liability. As stepwise liabil-
ity is tied to the procedural progression of the case, it enables the plaintiff to receive partial compensation
relatively quickly, by dropping and cashing in after surviving the f‌irst steps. This feature should be con-
trasted with the proportional rulewhich also grants partial compensation, but only after a complete trial.
This characteristic facilitates access to justice to f‌inancially-constrained plaintiffs.
1. In early works, the proportional rule was de f‌ined as referring to probability of causation—‘the measure of damages multiplied
by the probability that the liable party caused the harm(Shav ell, 1985: 589; see also Rosenberg, 1984). But the proportional
rule can easily be applied to any source of uncertainty surro unding the case (e.g., Abramowicz, 2001: 235236). For our pur-
poses, then, the proportional rule could be de f‌ined as a black-boxprobability that the defendant is liable. Cf. Tuzet an d
Esposito (2023: 330331).
280 The International Journal of Evidence & Proof 27(4)

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