Lessons from Grandfather

Abstract

Assume that, even with a time machine, Tim does not have the ability to travel to the past and kill Grandfather. Why would that be? And what are the implications for traditional debates about freedom? We argue that there are at least two satisfactory explanations for why Tim cannot kill Grandfather. First, if an agent’s behavior at time t is causally dependent on fact F, then the agent cannot perform an action (at t) that would require F to have not obtained. Second, if an agent’s behavior at time t is causally dependent on fact F, then the agent cannot perform an action (at t) that would prevent F from obtaining. These two explanations have distinct upshots for more traditional debates over freedom. The first implies that causal determinism is incompatible with the ability to do otherwise and also raises questions about the traditional arguments for the incompatibility of divine foreknowledge and the ability to do otherwise; the second does neither. However, both explanations imply that the Molinist account of divine providence renders agents unable to do otherwise, at least in certain circumstances.

Keywords

• time travel
• grandfather paradox
• ability
• freedom
• fixity