Libertarian free will defined: the ability to choose among alternative options compatible with one's nature. Two versions — principle of alternative possibilities (PAP) and sourcehood freedom.

Stratton defines libertarian free will (not political): (1) PAP — principle of alternative possibilities: genuine ability to have chosen otherwise (chocolate vs. vanilla at the ice cream shop); (2) Sourcehood freedom — you are the uncaused source of a specific thought or action, with no external causal determination. His combined definition: "the ability to choose between or among a range of alternative options each of which is compatible with one's nature at a given moment." Compatibilism says only one option is compatible with your nature at a given moment — Stratton asks why think that?