I'm writing this comment after coming up with my probability level but before reading anyone else's responses.

Until Yvain's question, I had not put a number on this. I suspect if there were a machine that could measure how confident I "really" am, it would show a higher number.

I spent less than a minute translating from my previous estimate of "highly confident but not certain" to a percentage. Things I considered that made the probability higher:

• Every time humans have figured out how something works, the explanation has been a reductionist one.
• The only reason to think that the mind would be an exception to this is that the mind is unique in other ways (qualia/subjective experience; free will).

Things I considered that made the probability lower:

• The proposition under question could be false for two different reasons:
  • ontologically basic mental entities
  • physical yet non-neurological parts of the mind's substrate
• I don't know how the mind works (nor does anyone else), so I should nudge my probability estimate away from certainty either way.
• The mind is indeed unique.