Full Idea
Why do we have need of a doctrine of the soul grounded merely on pure rational principles? Without doubt chiefly with the intent of securing our thinking Self from the danger of materialism.
Gist of Idea
We need an account of the self based on rational principles, to avoid materialism
Source
Immanuel Kant (Critique of Pure Reason [1781], B406-/A383)
Book Reference
Kant,Immanuel: 'Critique of Pure Reason', ed/tr. Guyer,P /Wood,A W [CUO 1998], p.433
A Reaction
And why is materialism a 'danger'? Only, I think, because it would make immortality impossible. Huge chunks of Enlightenment philosophy are the last vestiges of the religious view of reality. I think we can base morality on a material self.