Libet? Non Liquet.
Some have claimed that Libet’s experiment proves that human beings do not have free will. I doubt that the experiment proves so.
Let’s set aside questions about the accuracy of the experiment with respect to precisely when people claimed to make a decision to move. Let’s also ignore the objection that even if the experiment had shown that the persons moving their hands didn’t do so freely on those occasions, it wouldn’t follow that no human being ever does anything freely.
Libet’s experiment provides some evidence that brain activity influences our choices. But his experiment doesn’t prove that brain activity causally determines our choices. There’s a significant difference between influencing and causally determining.
For example, note the distinction between desiring and willing. To desire x is to have a felt inclination or urge to x. To will x is to choose x. One can desire x yet not choose it, such as when one wants to eat a cookie but chooses not to. And one can choose x yet not desire it, such as in the case of one choosing to keep his promise to help his friend move at 5 AM on Saturday despite the fact that he desires not to help but rather to stay in bed. As Kant noted long ago, the moral evaluation of our actions has much to do with one’s willingness to perform one’s duty regardless of one’s desires, and indeed even if one’s desires oppose the performance. In any case, arguably, a desire to x does not cause one to choose x, though one can choose x on the basis of non-determining reasons which include a desire to x. Hence, a desire to x might influence the choice to x and yet not causally determine x.
Now, it is consistent with Libet’s experiment to hold that the brain activity recorded was the sort of activity that occurs when one wants to move one’s hand. That type of desire might have influenced the experimentee’s choice to move his hand, or perhaps it didn’t influence the choice. In either case, the brain activity associated with the desire is not identical to the choice. Assuming that the desire didn’t cause the choice, it is an open question that the choice might be free despite the fact that it was preceded by the brain’s desiderative activity.