For us there is only the trying. The rest is not our business.
T.S. Eliot, Four Quartets
Few arguments in contemporary philosophy have had more influence than Harry Frankfurt's ‘Alternate Possibilities and Moral Responsiblity.’ In that famous paper Frankfurt noted that all parties to the traditional debate about the compatibility of free will and moral responsibility with determinism had subscribed to a common assumption. They had assumed the truth of something Frankfurt called ‘the Principle of Alternate Possibilities,’ which he expressed as follows:
(PAP) A person is morally responsible for what he has done only if he could have done otherwise.
In the traditional debate incompatibilists argued that if determinism is true, then no one can ever do otherwise, while compatibilists argued that there is a morally relevant sense in which even a deterministic agent can do otherwise. Frankfurt proposed to show that PAPis false, thereby undercutting the traditional debate.