Free Will - What Is It and Does It Exist?

[InJoy]

From another thread, this fascinating subject arose.

Does free will exist? Can the actions of people ever be accurately predicted 100% of the time? If there was enough computing power and underlying data, could we ever predict the future with accuracy? Do we have a choice about what we do, or is it predetermined? If free will does exist, is it limited to humans?

There are probably dozens more questions.

Let's start with the one Michael Chui asked me:

Define "free will" and/or "choice".

Wordnet Princeton defines free will this way: the power of making free choices unconstrained by external agencies
It defines choice (in this context) as: the act of choosing or selecting

To me, free will is the ability to choose freely, even randomly, whenever I want. By this definition (if we can agree upon it) it is the opposite of determinism. In other words, the future is unpredictable. It would be impossible to predict with 100% accuracy what's going to happen tomorrow because people (at least) have the ability to change their minds and actions at will.

Anybody have a better definition?