By Randy Pausch

I have an engineering problem. While for the most part I'm in terrific physical shape, I have ten tumours in my liver and only a few months left to live. I am a father of three young children, and married to the woman of my dreams.

So, how to spend my very limited time? The obvious part is being with, and taking care of, my family. The less obvious part is how to teach my children what I would have taught them over the next 20 years. My desire to do that led me to give a “last lecture”.

A lot of professors give talks titled “The Last Lecture”. It has become a common exercise on American college campuses. Professors are asked to ruminate on what matters most to them. And while they speak, audiences can't help but mull over the same question: if we had to vanish tomorrow, what would we want as our legacy?

Last year, at Carnegie Mellon in Pittsburgh, where I am Professor of Computer Science, I was given the September slot. I already had pancreatic cancer diagnosed, but I was optimistic. Maybe I'd be among the lucky ones who'd survive.

In mid-August, however, I got the news: my most recent treatment hadn't worked. I had just months to live.

I knew I could cancel. Everyone would understand. And yet, despite everything, I couldn't shake the idea of giving the talk.

“They'll let me back out,” I told my wife, Jai, “but I really want to do it.”

Jai had always been my cheerleader. But we had just moved from Pittsburgh to southeast Virginia so that after my death, she and the kids could be near her family.

“Call me selfish,” Jai told me. “But I want all of you. Any time you'll spend working on this lecture is lost time, because it's time away from the kids and from me.” There was another matter upsetting Jai: to give the talk, I would have to fly to Pittsburgh on her 41st birthday. “This is my last birthday we'll celebrate together,” she told me. “You're actually going to leave me on my birthday?”

Given Jai's reticence, I had to look honestly at my motivations. Was this talk a limelight lover's urge to show off one last time? The answer was yes. But there was something else. I reminded Jai of the kids' ages: 5, 2 and 1. “Look,” I said. “At 5, I suppose that Dylan will grow up to have a few memories of me. But how much will he really remember? And how about Logan and Chloe? They may have no memories at all. Nothing.

“Especially Chloe. And I can tell you this: When they are older, they're going to need achingly to know: ‘Who was my dad?' This lecture could help to give them an answer to that.” Jai smiled at me, her dying showman, and finally relented.

And so, with Jai's green light, I had a challenge before me. I didn't want the lecture to focus on my cancer. Cancer didn't make me unique. My uniqueness, I realised, came in the dreams - from incredibly meaningful to decidedly quirky - that defined my 46 years of life. I had managed to fulfil almost all of them because of things I was taught by extraordinary people along the way.

My mother was a tough, old-school English teacher with nerves of titanium. Her high expectations became my good fortune. My dad was a Second World War medic who later ran a small car insurance business in inner-city Baltimore. For a million reasons, he was my hero.

Money was never an issue in our house, mostly because my parents never saw a need to spend much. We rarely went out to dinner. We'd see a movie maybe once or twice a year. “Watch TV,” my parents would say. “It's free. Or better yet, go to the library. Get a book.” It sounds oppressive by today's standards, but it was a magical childhood. Growing up, I thought there were two types of families:

1. Those who need a dictionary to get through dinner. 2. Those who don't.

We were No 1. “If you have a question,” my folks would say, “then find the answer.” Open the encyclopedia. Open the dictionary. Open your mind.

My dad seemed to know everything. My mother, meanwhile, knew plenty, too. All my life, she saw it as part of her mission to keep my cockiness in check.

When I was studying for my PhD, I took something called “the theory qualifier”, which I can now definitively say was the second worst thing in my life after chemotherapy. When I complained about how awful the test was, she leant over, patted me on the arm and said, “We know just how you feel, honey. And remember, when your father was your age, he was fighting the Germans.” In 1969, when I was 8, my family went on a cross-country trip to Disneyland. As I stood in line with all the other kids, all I could think was “I can't wait to make stuff like this!” Two decades later, when I got my PhD, I dashed off my letters of application. And Walt Disney Imagineering sent me some of the nicest go-to-hell letters I'd ever received. That was a setback. But I believe brick walls are there for a reason. They're not there to keep us out. They are there to give us a chance to show how badly we want something.

Fast-forward to 1995. I'd become a professor at the University of Virginia, and I'd helped to build a system called “Virtual Reality on Five Dollars a Day”. I learnt that Disney Imagineering was working on a virtual reality project. It was a top secret Aladdin attraction that would allow people to ride a magic carpet. I called Disney, was ridiculously persistent, and eventually was connected to a guy named Jon Snoddy. He happened to be the brilliant Imagineer running the team. After we chatted a while, I told Jon I'd be coming to California. Could we get together? He told me OK. We could have lunch.

At the end of the lunch, I made “the ask”. It was almost unheard of for Imagineering to invite an academic inside its secretive operation, but he thought it would be a fine idea if I took a sabbatical to work with them.

It was a fantasy come true. In fact, I have a confession. This is how geeky I am: soon after I arrived in California, I drove over to Imagineering headquarters with the soundtrack to Disney's The Lion King blasting on my stereo. Tears actually began streaming down my face as I drove past the building.

Here I was, the grown-up version of that wide-eyed eight-year-old at Disneyland. I had finally arrived.

The most formidable brick wall I ever came upon was just 5ft 6in tall, and absolutely beautiful. But it reduced me to tears. That brick wall was Jai. We met in the autumn of 1998, when I gave a lecture at the University of North Carolina. I was a 37-year-old bachelor who had spent a lot of time having great fun, and then losing girlfriends who wanted to get more serious. Jai was a 31-year-old comparative literature student working part-time in the computer science department.

Her job was to host visitors and on that day, her job was to host me. I was completely taken with her. I had to go to a formal faculty dinner that night, but I asked if she'd meet me for a drink afterwards. She agreed.

During dinner I wished all those professors would just chew faster. I convinced everyone not to order dessert. And I got out of there at 8.30 and called Jai.

We went to a wine bar and ended up having a terrific time.

After I returned to Pittsburgh, I asked Jai to visit me. She was scared of my reputation and of the possibility that she was falling in love.

“I'm not coming,” she wrote in an e-mail. “I've thought it through and I'm not looking for a long-distance relationship. I'm sorry.” This was a brick wall I could manage. I sent her a dozen roses and a card that read: “Although it saddens me greatly, I respect your decision and wish you nothing but the best. Randy.” She got on the plane.

We saw each other almost every weekend through the winter and, eventually, I asked her to move to Pittsburgh. I knew she was still scared but she did agree to moving up and getting her own apartment.

In April, however, Jai told me: “I'm sorry. This will never work. I just don't love you the way you want me to love you.” And then again, for emphasis: “I don't love you.” I was heartbroken. Could she really mean that?

I spent much of the rest of that day on the phone to my parents, telling them about the brick wall I'd just smashed into. Their advice was incredible. “Be supportive,” my mom said. “If you love her, support her.” And so I spent that week hanging out in an office up the hall from Jai.

I stopped by a couple of times, however, just to see if she was all right. “I just wanted to see how you are,” I'd say. “If there's anything I can do, let me know.” A few days later, Jai called. “Well, Randy, I'm sitting here missing you. That means something, doesn't it?” She was in love, after all.

Brick walls are there for a reason. They give us a chance to show how badly we want something.

There are so many things I want to tell my children, and right now, that they're too young to understand. Dylan just turned 6. Logan is 3. Chloe is 18 months old. It pains me to think that they won't have a father. When I cry in the shower, a percentage of my sadness is, “I won't, I won't, I won't...” But a bigger part of me grieves for them.

I keep thinking: “They won't... they won't... they won't.” That's what chews me up inside, when I let it.

I know their memories of me may be fuzzy. That's why I'm trying to do things with them that they'll find unforgettable.

Dylan and I went to swim with dolphins. When a kid swims with dolphins, he doesn't easily forget it. I'm going to bring Logan to Disney World, a place that I know he'll love as much as I do.

I'm aware that Chloe may have no memory of me at all. But I want her to grow up knowing that I was the first man ever to fall in love with her. I'd always thought the father/daughter thing was overstated. But I can tell you, sometimes, she looks at me and I just become a puddle.

When they're older. Jai might talk to them about my optimism, the way I embraced having fun, the high standards I tried to set in my life. She may diplomatically tell them some of the things that made me exasperating; like my insistence (too often) that I know best.

But she's modest, and she might not tell the kids this: that in our marriage, she had a guy who deeply, truly loved her. “Lucky” is a strange word to describe my situation, but a part of me does feel fortunate. Cancer has given me the time to have vital conversations with Jai that wouldn't be possible if my fate were a heart attack or a car accident.

What are we talking about? We both try to remember that some of the best advice we have ever heard comes from flight attendants: “Put on your own oxygen mask before assisting others.” Jai knows that she will have to give herself permission to make herself a priority. I've also reminded her that she's going to make mistakes. If I were to live, we would be making them together and she shouldn't attribute them all to the fact that she'll be raising the kids herself.

It's possible that she will find the children's teenage years the most challenging. Having been around students all my life, I'd like to think that I would come into my own as a father. So I'm sorry I won't be there.

The good news, though, is that other people - friends and family - will want to help, and Jai plans to let them.

As for the obvious question, well, here's my answer: most of all, I want Jai to be happy. If she finds happiness through remarriage, that will be great. If she finds happiness without remarrying, that also will be great.

As I prepared to give my last lecture, I wanted some way to show how much I love and appreciate Jai. Near the end, I arranged to have a large birthday cake with a single candle wheeled on to the stage. I explained that I hadn't given Jai a proper birthday, and thought it might be nice if I could get 400 people to sing to her. They applauded and began singing Happy Birthday.

I had no idea what I would do or say after that. But as Jai came towards me on the stage, impulse took over. We embraced and kissed. The crowd kept applauding.

We heard them, but it was like they were miles away. As we held each other, Jai whispered something in my ear. “Please don't die.” It sounds like Hollywood dialogue. But that's what she said. I just hugged her more tightly.

© Randy Pausch 2008. Extracted from The Last Lecture by Randy Pausch with Jeffrey Zaslow, to be published by Hodder & Stoughton on April 17 at £12.99. It is available from Times BooksFirst for £11.69. 0870 1608080, timesonline.co.uk/booksfirst