 If possession of free will requires an ability to act otherwise than one in fact does, then it is fairly easy to see why free will has often been regarded as incompatible with causal determinism. One way of getting at this incompatibilist worry is to focus on the way in which performance of a given action should be up to an agent if he has the sort of free will required for moral responsibility. As the influential Consequence Argument has it (Ginet 1966; van Inwagen 1983: 55–105; Wiggins 1973), the truth of determinism seems to entail that an agent’s actions are not up to him since they are the unavoidable consequences of things over which the agent lacks control. Here is an informal summary of this argument from Peter van Inwagen’s important book, An Essay on Free Will (1983):