Full Idea
The existence of an immaterial 'intellective soul' ..cannot be demonstrated; for every reason by which we try to prove it assumes something that is doubtful for a man who follows only his natural reason. Neither can it be proved by experience.
Gist of Idea
There are no secure foundations to prove the separate existence of mind, in reason or experience
Source
William of Ockham (Seven Quodlibets [1332], I Q x)
Book Reference
Ockham,William of: 'Ockham's Philosophical Writings', ed/tr. Boehner,P [Hackett 1990], p.142
A Reaction
This is splendid honesty from a medieval monk. How would such a clear thinker have responded to modern brain research? Colin McGinn still maintains William's view, despite modern knowledge. Our ignorance produced conceptual dualism.