Full Idea
How any thought should produce a motion in body is as remote from the nature of our ideas, as how any body should produce any thought in the mind.
Gist of Idea
Thoughts moving bodies, and bodies producing thoughts, are equally unknowable
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 4.03.28)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.559
A Reaction
Compare McGinn's Idea 2540. Locke was a thoroughgoing Mysterian, but in his case it was part of a widespread pessimism about penetrating any of the inner secrets of nature. Modern Mysterians see it as the one secret we can't get.
Related Idea
Idea 2540 Examining mind sees no brain; examining brain sees no mind [McGinn]