The Supreme Court ruling this week on the liability of the family of a 91-year-old dementia patient fatally hit by a train after wandering onto the railway tracks in 2007 should lead us once again to think who should bear — and how society should share — the burden of caring for the expanding ranks of the elderly requiring nursing in this rapidly aging country.

The man in Obu, Aichi Prefecture, who was suffering from a severe case of Alzheimer's disease, disappeared from his home while his 85-year-old wife was taking a brief nap. He took a train and got off at the next station, wandered onto the tracks by opening the fence at the end of the platform, and was hit and killed by a train. The railway sued the man's wife and his son for ¥7.2 million in compensation to cover the cost of dealing with the accident, including the expense of providing alternate transportation for passengers.

Lower courts ordered the family members to pay the damages, on the grounds that they bore the responsibility of keeping watch over the man, who had repeatedly wandered away from home. In a landmark ruling Tuesday, the Supreme Court relieved both the widow and the son of their duties to pay the compensation, saying their liability should not be determined by family ties alone but require a comprehensive judgment on whether it was practically possible for the relatives to watch over the man's actions. Along with the son, who had been living away from the parents for more than 20 years, the wife — who lived with the man in the house — cannot be deemed to have been capable of supervising the husband's behavior since her own failing health required nursing care, the top court said.