Every 90 days I lie in a whirling CT machine, dye coursing through my veins, and the doctors look to see whether the tumors in my liver are growing. If they are not, the doctors smile and schedule another scan. The rhythm has been the same since my doctors told me I had stage IV colon cancer two and a half years ago. I live for three months, take a deep breath and hope to start over again. I will probably do this for the rest of my life. Whatever that means.

Let us consider me as a test case. As I have said, I would like to die peacefully with Thomas Tallis on my iPod before the disease takes me over and I hope that will not be for quite some time to come, because if I knew that I could die at any time I wanted, then suddenly every day would be as precious as a million pounds. If I knew that I could die, I would live. My life, my death, my choice.

I live by the day. Just sitting in the park, looking at the flowers thinking how beautiful they are. It's almost … not hallucinogenic but it's a much stronger feeling than previously. For me, at the moment, going for a walk in the park with Gail is heaven.

I feel a sudden clear focus and perspective. There is no time for anything inessential. I must focus on myself, my work and my friends. I shall no longer look at “NewsHour” every night. I shall no longer pay any attention to politics or arguments about global warming. This is not indifference but detachment — I still care deeply about the Middle East, about global warming, about growing inequality, but these are no longer my business; they belong to the future. I rejoice when I meet gifted young people — even the one who biopsied and diagnosed my metastases. I feel the future is in good hands.

I rolled back the images. Looked again. There it was. A new tumor, large, filling my right middle lobe. It looked, oddly, like a full moon having almost cleared the horizon. Going back to the old images, I could make out the faintest trace of it, a ghostly harbinger now brought fully into the world. I was neither angry nor scared. It simply was. It was a fact about the world, like the distance from the sun to the Earth.

Everyone succumbs to finitude. I suspect I am not the only one who reaches this pluperfect state. Most ambitions are either achieved or abandoned; either way, they belong to the past. The future, instead of the ladder toward the goals of life, flattens out into a perpetual present. Money, status, all the vanities the preacher of Ecclesiastes described, hold so little interest: a chasing after wind, indeed.

I remember the moment when my overwhelming uneasiness yielded. Seven words from Samuel Beckett, a writer I’ve not even read that well, learned long ago as an undergraduate, began to repeat in my head, and the seemingly impassable sea of uncertainty parted: “I can’t go on. I’ll go on.” I took a step forward, repeating the phrase over and over: “I can’t go on. I’ll go on.” And then, at some point, I was through.

Yet one thing cannot be robbed of her futurity: my daughter, Cady. I hope I’ll live long enough that she has some memory of me. Words have a longevity I do not. I had thought I could leave her a series of letters — but what would they really say? ... There is perhaps only one thing to say to this infant, who is all future, overlapping briefly with me, whose life, barring the improbable, is all but past. That message is simple: When you come to one of the many moments in life when you must give an account of yourself, provide a ledger of what you have been, and done, and meant to the world, do not, I pray, discount that you filled a dying man’s days with a sated joy, a joy unknown to me in all my prior years, a joy that does not hunger for more and more, but rests, satisfied.