Full Idea
My body is the only object of which I know not merely the one side, that of the representation, but also the other, that is called 'will'.
Gist of Idea
I know both aspects of my body, as representation, and as will
Source
Arthur Schopenhauer (The World as Will and Idea [1819], I 125), quoted by Christopher Janaway - Schopenhauer 3 'Will'
Book Reference
Janaway,Christopher: 'Schopenhauer' [OUP 2002], p.40
A Reaction
I'm not convinced that knowledge of the body through the will (and action, presumably) constitutes a different sort of knowledge. Philosophers are always trying to split the world in two (but not Nietzsche!).