[Patrick Logan, a freelance writer in New Hampshire, is writing a book about his relationship with his father.]

The third conditional in English grammar is used to imagine a hypothetical past. It's a structure I've thought about a lot recently while reading the letters my father sent my mother during World War II.

Italian King Victor Emmanuel III handed over power to Mussolini on Oct. 28, 1922, one week after my father was born. Two decades later he and the men of his generation were on transport ships bound for destinations from which many would not return. Had they been born just a few years later, their experience of the war probably would have been limited to newsreels.

In 1943, three years after completing a barbering course, my father found himself in boot camp. He wrote to my mother, boasting of his good fortune: "I don't know whether they recognized me as lazy or what, but I certainly got a snap job. No gun, no equipment, nothing. I cut hair and have to be a nice little boy among the books and ping pong tables."...