Full Idea
A philosophy of any subject (a system of rational knowledge from concepts) requires a system of pure rational concepts independent of any conditions of intuition, that is, a metaphysics.
Clarification
'Intuition' is here (roughly) experience
Gist of Idea
For any subject, its system of non-experiential concepts needs a metaphysics
Source
Immanuel Kant (Metaphysics of Morals II:Doctrine of Virtue [1797], 375 Pref)
Book Reference
Kant,Immanuel: 'The Metaphysics of Morals', ed/tr. Gregor,Mary [CUP 1991], p.181
A Reaction
'Pure rational concepts' must be a priori, and (in Kant's case) transcendental - i.e. discovered from the study of presuppositions. Does this actually say that the philosophies of science, biology, psychology, economics etc each needs a metaphysics?