I was once given an excellent definition of creativity by a trainer:
Creativity is the ability to combine things in a way no one else has ever thought of before.
Now, consider that for a while. You'll notice is that it is
postmodern and that it is inextricably connected to the
Neisser's Perceptual Circle.
We live in a postmodern world where our ideas are always influenced by others, perhaps someone has even figured them out already. Combine that idea with Neisser's Perceptual Circle which states that all our new conceptions are influenced by our earlier conceptions, rendering us less open to new ideas.
The definition arises naturally from these basic principles. There is no known mechanism for creating totally new schemes of thought - therefore all we can do is combine old ideas in new ways.