Mitigation, Avoided Loss, and Time of Assessment

AuthorJamie Cassels
1) Introduction
Mitigation of damages is the pr inciple that a plaintiff may not recover
losses that could have been avoided by ta king reasonable steps after the
wrong. The principle applies in both tort and contract. The Supreme
Court of Canada has quoted with approval the following statement
from the House of Lords:
The fundamental b asis is thus compen sation for pecuniar y loss nat-
urally f‌lowing f rom the breach; but this f‌irst principle is qu alif‌ied by
a second, which impose s on a plaintiff the duty of t aking all rea son-
able steps to mitigate the loss con sequent on the breach, and debar s
him from claim ing any part of the damage which i s due to his neglect
to take such steps.1
Another way of expressing t he rule is that a plainti ff cannot recover
“avoidable losse s.”2
1 British Westinghouse Electr ic & Manufacturing Co Ltd v Underground Electr ic Rlys
Co of London Ltd, [1912] AC 673 at 689 (H L) [British Westinghouse], quoted wit h
approval in Asame ra Oil Corp v Sea Oil & General Corp (1978), [1979] 1 SCR 633
at 661 [Asame ra].
2 Red Deer College v Michaels, [1976] 2 SCR 324 [Red De er College].
Mitigation, Avoided Loss, a nd Time of Assessment 429
There are sound reasons underlying t he obligation to mitigate.
Most generally, mitigation is about fairness. It will be recalled that the
fundamental premi se of this book is that civ il remedies are intended
to do justice between the part ies, and that damages should be set at a
level that properly protects the plaintiff’s interests without being un-
duly oppressive to the defendant. Damages are not generally i ntended
to be punitive. Following a tort or breach of contract, the plaintiff may
not hold the defendant hostage to every loss that might occur. Where
the plaintiff i s reasonably able to avoid a loss, or to take steps to mini-
mize it, it would be antisocia l and punitive for the plaintiff to sit back
and do nothing, thus incurring an “unconscionable accumulation”3
of damages. The rule of mitigation ha s the effect of minimizing the
total costs of the tort or breach of contract, thereby avoiding unduly
burdening or surprising the defendant with an unexpected extent of
liability. It should be borne in mind that not all breaches of contract a re
mala f‌ides or even intentional. There is no general policy that contract
breach should be punished. Similarly, most torts involve the unintend-
ed consequences of legitimate activ ities. The rule of mitigation ref‌lects
a recognition that “accidents happen” and that no usef ul purpose is
served by allowing the damages to increase in their aftermath.
The basic insight that it is soci ally desirable to minimize the total
costs of a civil wrong has been formalized by legal economists. The
rule of mitigation is said to be eff‌icient in that it provides an incentive
to minimize the joint costs of an activity. More specif‌ically, in breach
of contract cases, mitigation per mits “eff‌icient breach.” According to
this notion, where the cost to the promisor of performing a contract is
substantially more ex pensive than the loss to the other party from non-
performance, the contract should not be performed. It is uneconomic,
and oppressive, to force completion of such contracts when any losses
to the innocent party c an be compensated by damages. The theory also
applies when the promisor is able, by breaching, to ear n additional
prof‌its on an alternate tran saction. Where the innocent party’s loss can
be fully compensated by an awa rd of damages paid out of the additional
prof‌its, and there is still a net gain to b e earned on the alternate trans-
action, it is eff‌icient (joint value is maximized) to permit the breaching
party to pursue the alternative transaction.4 The rule of mitigation, re-
quiring the in nocent party to take steps to keep the costs of breach low,
further promotes this result.
3 Ibid.
4 RA Posner, Economic Analysis of L aw, 6th e d (New York: As pen, 2003) at 120.
The Supreme Court of Cana da has approved the idea of eff‌icient br each: Bank of
America Cana da v Mutual Trust Co, [2002] 2 SCR 601 at pa ra 31.
The rule of mitigation also ensure s a fair allocation of risks between
the parties. Often t he plaintiff is in t he best (or only) position to deal
with the consequences of a breach of contract or tort. In such circum-
stances, it would be wrong to saddle defendants w ith post-breach risks
over which they have no control. For example, where a buyer of goods
breaches a contract of sale, the vendor has an obligation to resell the
goods. If the vendor does not do so and the goods spoil, or the ma rket
price falls, that additional loss is caused as much by the vendor’s in-
action as by the buyer’s breach. Additionally, while the vendor in such
a case may choose to hold onto the goods rather t han to resell them (in
the hope that the market price will increase), the risk of such specula-
tion should generally fall on the plaintif f’s shoulders rather than the
defendant’s (if the price does in fact increase, the plaintiff will be per-
mitted to retain the prof‌it).
2) General Principles: Reasonableness
The objective of the rule of mitigation is to give the plainti ff an incen-
tive to take steps to minimize the total costs of the tort or breach of
contract, and to avoid unduly burdening the defendant with avoid-
able losses. The plaintiff is deba rred from recovering losses t hat could
reasonably be avoided. What is rea sonable is a question of fact, not law,
and the burden of proof is upon the defendant to demonstrate that
the plaintiff could rea sonably have avoided a loss or was unreasonable
in her conduct.5 In assessing reasonableness, t he context is import-
ant. In the commercial context, plai ntiffs must do what an ordinar y
business person would do in the circumstances. They must take ac-
tions that are consistent w ith their usual practices and may not let their
feelings of hostility or anger get in the way. However, the plaintiff is
not obliged to make extraordinar y efforts, to take ser ious business
risks or gambles, or risk its reputation or business relationships to
reduce a loss.6 The plaintiff need only do what is prudent under the
5 Red Deer Coll ege, above note 2; Coutts v Brian Jessel Autosport Inc (2005), 40
CCEL (3d) 236 (BCCA); Proctor Crushing Inc v Precision Surfac ing Ltd, 2004
ABQB 713 at paras 72 –73 [Proctor Cru shing]; 2438667 Manitoba Ltd v Husky Oil
Ltd, [2007] MJ No 233 (CA); Ke rn v Steele (2003), 220 NSR (2d) 51 (CA); BP
Global Special Product s (America) Inc v Conros Corp, 2010 ONSC 1094 at p ara 68,
aff’d 2011 ONCA 384.
6 For example, see 3Com Corp v Zorin Inter national Corp, [2006] OJ No 2184 (CA),
where the court held t hat the plaintiff, a v ictim of fraud, did not need to be
overly aggres sive with its other (innocent) custome rs in revoking sales rebate s
that it would not have given b ut for the fraud.

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