Arizona statutes require a common liability for the same injury as a predicate for the allocation
of fault among parties and non-parties under A.R.S. § 12-2501.
In the case of multiple acts, is there a single, indivisible injury that gives rise to common
The Restatement (Third) of Torts focuses primarily on whether there is a reasonable basis to
divide liability based on causation, but distinguishes division by causation from apportionment
of responsibility. Division by causation is the process by which one reduces a group of injuries
which constitute indivisible injuries. Only after that is done is responsibility for each indivisible
This is illustrated by two decisions. In Potts v. Litt, 171 Ariz. 98,828 P.2d 1239 (App. 1991),
Potts was involved in two automobiles collisions, 13 days apart. The court concluded that “even
though it might have been difficult to apportion Potts’ damages, it was not impossible.” 171
Ariz. at 100,828 P.2d at 1241. By the new Restatement view, it was possible to divide the
damages by causation and unnecessary to apportion the responsibility, meaning that the case
should have been litigated as essentially two separate claims against two separate defendants for
two separate injuries. There was no common liability.
Piner v. Superior Court, 192 Ariz. 182, 962 P .2d 909 ( 1998), faced the same issue, but after the
abolition of joint and several liability. Piner was hurt in a rear-end auto accident in the morning
and called his doctor complaining of specific injuries. The doctor’s staff told him to call back in
the afternoon. However, in the afternoon he was rear-ended again, called the doctor again, and
complained of additional pains in the same parts of the body. Unquestionably both collisions
contributed to his injuries. Piner argued that because there was an indivisible injury, the liability
of both tortfeasors was joint and several.
The Supreme Court concluded that the indivisible injury rule survived despite the abolition of
joint and several liability, relieving the plaintiff of apportioning damage according to causal
contribution. If the facts make divisibility of the injury impossible, once plaintiff established that
each tortfeasors contributed to his injuries, it was up to the defendants to establish who caused
what part of the injury. This means that the jury must apportion not damages, but fault, and must
do so for each accident. The plaintiffs recovery will be the total damage sustained and the jurors
will be instructed to allocate fault according to A.R.S. § 12-2506, i.e., for the amount of damages
in direct proportion to the defendant’s percentage of fault.
In practice, cases like Piner will be rare. Most successive cases involve a factual dispute over
whether the injury is indivisible. In that case the jury will first decide the division of damages,
then the apportionment of fault. They will attempt to apportion damages from two successive
accidents and then turn the page of the verdict form to find that they must then apportion fault for
the two accidents.