Libertarians hold that free action and moral responsibility are incompatible with determinism and that some human beings occasionally act freely and are morally responsible for some of what they do. Can libertarians who know both that they are right and that they are free make sincere promises? Peter van Inwagen, a libertarian, contends that they cannot—at least when they assume that should they do what they promise to do, they would do it freely. Probably, this strikes many readers as a (...) surprising thesis for a libertarian to hold. In light of van Inwagen's holding it, the title of his essay—‘Free Will Remains a Mystery’—may seem unsurprising. (shrink)