“In a way, the view that we are chained to our natures and the belief that we are products of external forces are diametrically opposed. One sees each human as a product of his or her own static character and disposition. The other sees each individual as an object on which circumstances act. Both see human behavior as constrained rather than free. One can be agnostic about whether internal or external forces are more influential in any given case and still acknowledge that the end result is limit rather than choice.”