Full Idea
Whatever conception of the freedom of the will one may form in terms of metaphysics, the will's manifestations in the world of phenomena, i.e. human actions, are determined in accordance with natural laws, as is every other natural event.
Gist of Idea
The manifest will in the world of phenomena has to conform to the laws of nature
Source
Immanuel Kant (Idea for a Universal History [1784], Intro)
Book Reference
Kant,Immanuel: 'Political Writings', ed/tr. Reiss,Hans [CUP 1996], p.41
A Reaction
So free will either requires total substance dualism, or it is best described as transcendental fictionalism. This seems to imply the Leibnizian idea that metaphysics contains facts which having nothing to do with the physical world.