Compatabilism is one approach to the problem of freewill in a casually closed world: How to reconcile freewill with a casually determined world (in particular one that follows the laws of physics)?
Incompatibilists hold that freewill cannot exist in a causally determined world: either we have freewill and the world is not causally deterministic, or conversely the world is causally deterministic and we do not have freewill.
Compatibilists hold that freewill and causal determinism are compatible (hence the name). They do this by redefining the concept freewill. As long as a person is free from external coercion, they are acting according to their own freewill. Another way to state the compatibilist position is to say that people have freewill as long as they are free to act according to their own motivations.
It seems to me that for the compatibilist approach to freewill to be workable - especially within the context of moral responsibility - they need to address the issue of insanity. In both social and legal contexts people who are deemed insane are considered to be not responsible for their actions. But from the compatibilist point of view they are free agents since they are not constrained by any outside forces in their behavior.
The social and legal perception of insanity seems to imply that an insane person isn't free to act according to their motivations because they have internal constraints (their psychiatric condition) on their actions as opposed to external ones.
Setting aside psychiatric definitions of insanity, I feel that compatibilists need to address this at a more fundamental level for their position to be consistent.
- Where does the boundary lie between actions that are free and actions that are constrained by mental health issues?
- How do we separate the legitimate motivations of a free agent from the delusional or mistaken motivations of an insane person?
- Is there an inner level of consciousness where the agent's true motivations lie?
- How do compatibists address insanity?