In a scramble to manage the growing distance between us, I worked her magic in reverse and gave her things to carry with her that would remind her of home, even though she was no farther away than school. I tucked notes into her flowered bag, I gave her my wallet, I made sure she had a little elastic-bound notebook like mine. I presented one memento after another, as she did when I left town, to make sure that we were together even when we weren’t. I did so with the increasingly bleak awareness that Sarah’s departures were different. For me, the best part of leaving was coming back. We had no guarantee that Sarah’s trajectory would bank into a similar return curve.

One day, on the way home from elementary school, we ran out of conversation before the traffic cleared, so I raised a question that had bedeviled generations of philosophy 101 students, including myself: If a tree falls in the forest, I asked Sarah, does it make a sound?

She looked at me as if I were mad.

Of course it does, she said.

I presented a counter-argument. What if sound requires a witness? If I said I’d bought a blue sweater, it undoubtedly wouldn’t be the same color as if Grandma said she’d bought a blue sweater, so maybe some part of color and sound, some part of what our senses perceived, resided inside us, not in the thing itself.

Now she knew I was nuts. She went on at some length in defense of her position; having mastered all of her senses far more recently than I had, she wasn’t about to abandon her hard-won notion of a universal order.

I’d mentioned the falling tree because Sarah liked puzzles, and I thought we’d dispatch it before we got home—but the conversation continued for years, off and on, with increasingly sophisticated references to sound waves and audio nerves, to tape recorders and surveillance equipment. No matter what the level of discourse, Sarah remained as firm as she had been in the car, that first day: Noise and the elements of the color wheel and lots of other things existed even if nobody was there to see or hear or touch or smell or taste them. Some things, she insisted, just are.

That was a while ago, when the simple fact that I had a driver’s license and she didn’t guaranteed that we would have plenty of time to chat. Now, at the start of her senior year in high school, a disproportionate number of those conversations have as their subject the coming shift in our family landscape. I struggle not to compile a list of what a friend with an older daughter calls “the lasts”—the last time we are guaranteed all holidays together at home, the last year we definitely will celebrate all of our birthdays in person, the last time I will take a first-day-of-school photograph of Sarah posed in the same place she’s stood every year for the past twelve. How will I persuade her to let me take a first-day photograph next year, and where will the new wall be?

I see that the fulcrum of her life was the college tour she went on over spring break in her sophomore year. It was the academic equivalent of speed-dating—a college every three hours!—and in truth, we sent her not so much to find a campus as to let her have ten days of fun with her pals. It worked. Before the ink on the check was dry, we were getting calls like this: “I’m on the corner of Sixth Avenue and Forty-fifth Street. Where’s the restaurant with that cheese and tomato thing?”

The pace picked up dramatically after that. The girl who had never evinced the slightest interest in sleepaway camp—or in spending more than the very rare night at a friend’s, for that matter—came home one afternoon with a brochure for a three-week summer program and didn’t call home as often as any of us had anticipated once she got there. The summer before her senior year, she found a four-week program in a city where she could see friends she’d made the previous year. Temptation was everywhere; suddenly colleges in cities neither Larry nor I had ever visited were sending seductive brochures addressed not to us but directly to our daughter—and she looked at them and started to construct a hierarchy of desire.

And we, the reluctant but dutiful coconspirators, bought her a file cabinet in which she could keep all the brochures and letters and applications, so that she would have an alphabetized plan for her escape at her very fingertips. As much as I didn’t like the idea of losing her for four weeks, I began to look forward to the summer program—as I might look forward to root canal, which would hurt temporarily but would protect me, down the line, from a world of pain. For I had come to understand the subtext of all these small departures: Whatever a program like this offered our children, it offered parents an honorable experiment in being alone. This was a chance to build up calluses so that the real thing wouldn’t hurt so much.

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