P stopped his truck to let a pedestrian cross the street. A car driven by Billy Jones hit P's truck from behind. Police were called to investigate the incident. P called his physician to complain of pain in his neck, upper back, left arm, and head. The doctor's staff told P that the doctor was unavailable but would call him back later that day. Piner then fixed the broken tail lights on his truck and went to work. P was driving to lunch when the car ahead of him stopped to let some pedestrians cross the street. P stopped and was again hit from the rear, this time by a vehicle driven by Cynthia Richardson. Feeling similar pain symptoms after this accident, P called his doctor's office and was again told that the doctor was occupied and would contact him later. The doctor concluded that P suffered a number of injuries as a result of the collisions. Due to the nature of the injuries, neither P's doctor nor any other physician has been able to attribute any particular part of P's total injuries to one accident or the other. P sued Ds alleging indivisible injuries resulting from the successive impacts. All parties agree that both collisions contributed to P's total physical injuries. P moved for partial summary judgment, arguing that because his injuries are indivisible, Ds should be held jointly and severally liable; Ds have the burden of proving apportionment; if neither defendant can demonstrate what portion of the total damage he or she caused, they should be held jointly and severally liable for the entire amount. The court denied P's motion. A new judge, who was going to do the trial, granted a continuance to allow P to file a special action in the nature of mandamus or prohibition to determine the propriety of the earlier ruling on apportionment; if P could not apportion the injuries, he was out of court. The court of appeals declined jurisdiction, but the Supreme Court granted certiorari.