Up until two weeks before her death, my mother drove her little Toyota through the streets of Boston every day. She couldn’t do it alone; my father had to help her. He guided her in and out of the car and turned the key in the ignition. Once, I saw him lean across to spin the wheel for her during a tight turn. My father didn’t drive himself. He was a semiretired merchant-marine officer who could navigate a cargo ship through crowded coastal waters, but in all my life I had never seen him behind the wheel of a car. Mom did all the driving. When my brother and I turned sixteen, we just kept on using public transportation. And by the spring of my first year in college, when my mother started showing the first signs of amyotrophic lateral sclerosis, or ALS, she was still the only driver in the house.