To have free will means that in some nontrivial sense persons are able to make choices that are not determined by causes other than themselves, so that each person may be regarded as the unique author of his or her own thoughts and actions. The term nontrivial indicates more than the absence of external and future determinants. A snowflake is free to fall until it hits the ground, but this freedom seems trivial. Free will implies the absence of internal or prior determinations.

Notions of free will involve two closely related ideas. Moral freedom is the idea that human being are morally responsible for their actions, and so may legitimately be praised or blamed, rewarded or punished. Metaphysical freedom amounts to the more radical claim that human choosing involves a break in the chain of physical causation. The human being is thus an indeterministic system, producing...