Henry David Thoreau once advised: "Go confidently in the direction of your dreams. Live the life you've imagined." With these encouraging words, David Heenan prefaces his new book Double Lives. The premise of the book as well as its conclusion, is that we can have a second, third or even fourth life. We can "follow our dreams" relatively often and quite successfully.

Author, artist, orator, soldier and statesman, Winston Churchill was all these and more. He is one of a number of people profiled by David Heenan in his recent book Double Lives. Mr. Heenan seems fascinated with such people who do not limit themselves to the narrow confines of one profession, but who rather dare to change.

Although having more than one career has become a recent trend, Mr. Heenan said that many years ago, he started doubting the myth of specialization as the only path to success and happiness.

"The idea really came to me almost 30 years ago," he recalled. "I just read Michael Crichton's The Andromeda Strain and was absolutely flabbergasted to learn that he actually had penned that best seller while between his second and third year of medical school at Harvard. As we all know, med school students probably have 10 minutes of discretionary time a day, and I was so impressed that somebody could crank out not only a best seller, but one that really set the pace for the whole techno-thriller genre. It got me interested in other people like Crichton, who are able to juggle two or more things at the same time."

In his book, Double Lives, David Heenan challenges the idea that 'the jack of all trades is the master of none.' Instead, he believes that an increasing number of people want more diversity in their lives.

Mr. Heenan says that the successful people he profiled in his book share common qualities, although they come from different walks of life.

"Certainly high energy is one element," he said. "They are all very curious. This goes back to Ben Franklin, to Da Vinci and Michaelangelo. I think all these people are really keen to probe into new waters. They, yet at the same time, have the ability, once they've gotten on something, to focus and concentrate on that field."

Among the successful people portrayed in Double Lives is Norio Ohga, whose love for electronics led him from the opera stage, as an operatic baritone, to the chairmanship of the Sony Corporation.

Sally Ride, the first woman astronaut, was about to become a pro tennis player before deciding to go ahead with her career in physics.

Ron Kent's story is another example of a successful life of more than one career. Mr. Kent grew up in Los Angeles where he was always encouraged by his parents to pursue multiple interests. After earning an advanced degree, he began a traditional career as an engineer. Eight years later, Mr. Kent abandoned the security of that high-paying job to become a stockbroker. Even before that, he had started a parallel career, an artistic one, as a wood sculptor.

"At first, as a young married couple, I was making furniture because we could not afford to buy it," he recalled. "Later, after both my income and ability had increased a little, we had enough furniture. I started dabbling in things that were more esthetic than useful. The actual 'artist' came almost as an accident. One day, I went to work at my brokerage office and they were taking entries for an art show in the shopping center across the street. So, I went home and got a piece that I had made for my own enjoyment, entered it and it was admitted into the show."

Mr. Kent's reputation as a wood sculptor has become well known and his work has earned him awards at home and abroad. For Ron Kent, to be an artist and engineer-turned stockbroker, he needed discipline and focus to balance life's competing needs.

But for Tess Gerritsen, a physician-turned-full time writer, it was quite impossible to balance the responsibilities of doctoring, writing and taking care of the family. So, in her mid-thirties, she retired from medicine to become, "a housewife writer." She started as a romance-novel writer. Eventually, she abandoned romance writing for bio-thrillers where her medical background has served her well. Harvest, her first bio-thriller, hit the New York Times best seller list in 1996. Paramount Pictures bought the film rights for $500,000, and the book has been translated into more than 20 languages. Since then, Ms. Gerritsen has published four more medical thrillers, generating millions of dollars in royalties and movie rights. She has no regrets about trading in the scalpel for the pen. However, she misses some aspects of her previous career as a physician.

"I miss meeting people and talking to people," she said. "But this career has allowed me to be much more fulfilled as a mother, I think."

Although having multiple careers is not confined to high-profile geniuses, it does take courage to change. It may mean sacrificing money, taking risks or losing job security. But author David Heenan, who himself leads a successful double life between business and academia, associates happiness with following dreams.

"The bottom line is that you find out that you are much more interesting to yourself and frankly to other people around you," he said. "I think that really is the payoff, that you're eliminating that nagging feeling that your life could be more fulfilling and that you are doing everything you can to maximize your potential."

David Heenan sums up what he considers the secret to successfully 'living all the lives you've imagined' by giving this simple advice: listen to your heart, take one step at a time, and never stop learning.