To illustrate how crystallized intelligence can operate, Gene D. Cohen, a founder of the field of geriatric psychiatry, related a story about his in-laws from his book “The Mature Mind: The Positive Power of the Aging Brain.” The couple, in their 70s, arrived in Washington for a visit during a snowstorm and found themselves stranded by the train station. When they saw a pizzeria across the street, his father-in-law had an idea. The couple went inside, ordered a pizza to be delivered to their daughter’s house, and then asked if they could ride along.