Full Idea
The generation of knowledge a priori, both according to intuition and according to concepts, and finally the generation of synthetic propositions a priori in philosophical knowledge, constitutes the essential content of metaphysics.
Gist of Idea
Metaphysics is generating a priori knowledge by intuition and concepts, leading to the synthetic
Source
Immanuel Kant (Prolegomena to Any Future Metaphysic [1781], 274)
Book Reference
Kant,Immanuel: 'Prolegomena to Any Future Metaphysic', ed/tr. Lucas,Peter G. [Manchester UP 1971], p.24
A Reaction
By 'concepts' he implies mere analytic thought, so 'intuition' is where the exciting bit is, and that is rather vague.
Related Idea
Idea 7919 Humeans rejected the a priori synthetic, and so rejected even Kantian metaphysics [Ayer, by Macdonald,C]