Given the spike in free-will debates on LW recently (blame Scott Aaronson), and the usual potentially answerable meta-question "Why do we think we have free will?", I am intrigued by a sub-question, "what would it feel like to have/not have free will?". The positive version of this question is not very interesting, almost everyone feels they have free will most all the time. The negative version is more interesting and I expect the answers to be more diverse. Here are a few off the top of my head, not necessarily mutually exclusive:

Epistemic:

• Knowing that someone out there already predicts my behavior perfectly
• Knowing that someone out there can predict my behavior perfectly, whether or not they actually bother doing it
• Knowing that it is potentially possible to perfectly predict my behavior, even if I know that no one is doing it
• Knowing that I am in a simulation 
• Knowing that I am in a simulation where repeated runs with the same inputs give identical outcomes
• ...?

Psychological:

• Feeling constrained by the environment to act in certain ways 
• Feeling constrained by the environment to act in certain unsatisfactory ways
• Voices in my head compel me to do things 
• Voices in my head compel me to do bad things 
• Feeling unable to complete thoughts I would like to think through, as if someone censored them
• ...?

Physical:

• Observing myself act in ways I never intended to act, whether beneficial to me or not
• Observing my arms/legs/mouth move as if externally controlled, and being unable to interfere
• ...?

For me personally some of these are close to the feeling of "no free will" than others, but I am not sure if any single one crosses the boundary.

I am sure that there are different takes on the answers and on how to categorize them. I think it would be useful to collect some perspectives and maybe have a poll or several after.