From Arnold Broese:

Re: Brain found to prepare decisions in advance (April 15): If these scientists are correct, and we have no free will, then (by their reasoning) their conclusions are not open to choice. They cannot choose to accept that what they think, is correct. That “choice” has already been determined for them according to pre-determined factors.

Validation of any theory requires that one is free to choose what evidence supports, or doesn’t support conclusions. Without free will, ‘truth’ ceases to exist, since one must be free to choose between the false and the truth.

All this aside, just as it is obvious that you don’t have to prove you are alive, since proof requires one to be alive, so it is with free will. To prove it, requires it.

Finally; one only has to introspect, and one can observe oneself making choices. That is all the evidence one requires.