Part of imagination for all three of these individuals was having the courage to come up with something completely new and defend it when others said, "It can't be so because we've never done it that way before." As stated before, they had the creativity to think outside the box and not allow their ideas to be restricted by any need to conform to what others considered to be true. They developed their ideas and stuck with them long enough for others to come to recognize the "correctness" of their work.
It might be easier to see how an author like Shakespeare used his imagination to achieve success, but the scientist and philosophers like Galileo and Einstein used just as much imagination in their work. During Galileo's time, people held very different beliefs about the way the world worked. Galileo imagined that the world was really a very different place. He worked hard to prove that what he imagined was reality. Einstein worked in a similar fashion with mathematics. He had to imagine that equations and such were there before he could prove how they worked. If it wasn't for Einstein's imagination, we wouldn't have many of the principles and equations we have today.
I think that all three of these characters used imagination actively rather than passively. It takes incredible imagination to come up with theories and different ways of looking at the world, and all three of these figures showed tremendous imagination in the way that they did not accept the status quo or the accepted way of thinking and could break out into new ideas and thoughts.
Without even looking at the other posts, my first response would be that they all were able to think "outside the box." No matter what was being done around them, and I'm certain they were aware, each was somehow able to offer something uniquely their own.
I doubt that most people would hesitate to connect the word "genius" to each of these men. My feeling, however, is not that it applies to how smart they were but to the kind of vision they had, and the courage they had to put themselves out in the public arena, regardless of whether what they shared was well-received or not. They each spoke "their piece," as only each could do. And while they were at it, they each changed the world.
Imagination is often something we think of with regard to storytellers and writers...artists. However, even though Shakespeare was a writer, he was so much more than a "storyteller." And Galileo and Einstein were able to use the flexibility of imagination to perceive what others were not able to. This is an interesting group of men to consider together.
Just about now, I also think I can't overlook Steve Jobs when I think of these men and this topic. What a legacy they all left behind: to change the face of the world in a positive way.
The preceding answers are all valuable. # 4 offers some interesting and thought-provoking comparisons and contrasts. Shakespeare did indeed use his imagination to invent some stories, although often he borrowed his plots from others. Even then, though, he had to adapt, modify, and adjust those sources to suit his own purposes. He also had to invent the actual, nitty-gritty phrasing of his works, and it is in the phrasing and other kinds of artistry that his true genius lies.
Galileo and Einstein had to "invent" in the sense that they had to imagine explanations for phenomena -- explanations that in many ways contradicted the accepted truths of their eras. This ability to imagine alternative explanations and then go about testing those imagined explanations shows that being a great scientist does not simply involve doing rote, routine, traditional experiments but often involves imagining revolutionary ways of understanding the universe.
Imagination is not always about sitting in a dark room and making things up. Galileo watched the tides going in and out and imagined a theory in which the movement of the Earth in space moved the massive fluid system of the oceans. Although he was incorrect about the cause of the tides, by necessity his model of the universe placed the Earth as a moving body instead of a stable center. This led directly to the scientific revolution that proved the Sun, not the Earth, was the center of the Solar system, as well as the eventual understanding of gravity and the Moon's influence on the tidal system. Of course, his imagination also led directly to his imprisonment and death, so it was more of a win/lose success.
Of these, Shakespeare is the most obvious. This was a man who had to imagine situations and characters and bring them to life in his writing. He did not make up the basic stories of all of his plays, but it was his imagination that created the very vivid characters and the memorable words that they spoke. In this way, his imagination allowed him to be successful.
"imagination" to you is a force of the creative individual, the artist. Many people don't realize that imagination comes into play whenever they take any idea and change it, however slightly, into something new.. Whenever you find a new way to use one or more objects, concepts or ideas, you are using your imagination. You are being creative. The creative aspect of yourself also known as imagination. If you have initiative and leadership you will begin to plan how to accomplish your goal. Select a task you do all the time. It could be as simple as making your bed. You may not think there are many ways to make a bed, but there are. You can begin at one corner or the other. You could straighten the bottom of the bed before you pull up the top, or straighten the top before the bottom. You could be begin at the right side instead of the left. If you want a real challenge, try making your bed with a pet or small child playing with you in the covers at the same time.When you do any task differently than is your habit, you are activating a different part of your brain. Imagination has always been with you.